At Park on Whiskey Road, we see the same off-season surprise every year: guests winterize perfectly—antifreeze, tanks drained, deep clean, seals checked—then open their rig in spring to a musty smell and a film of condensation on windows. The culprit is sneaky but simple: trapped humidity. Even a buttoned-up rig still has moisture in fabrics, cushions, and air.

As temperatures swing from cold nights to mild afternoons, that moisture condenses on cooler surfaces and lingers. The fix isn’t complicated, but it is deliberate. For many setups, an RV dehumidifier in winter storage is the missing step that protects interiors, stops mildew before it starts, and keeps your RV smelling fresh when camping season returns.

We’ll break down how moisture builds, which tools actually work in cold weather, and the easy habits that make the biggest difference, all from the perspective of a campground that helps travelers do this every season (and yes, we’re tipping our hat to a thoughtful piece on this topic from Do It Yourself RV).

Why moisture builds up in a closed RV

Even after you drain lines and seal openings, moisture remains in soft goods (mattress, upholstery, curtains) and in the air. When interior surfaces drop below the air’s dew point, that water vapor becomes liquid on windows, ceiling panels, and cabinet walls. Repeat that cycle all winter and you’ve got the classic “stored-RV” smell. If you want a quick refresher on the science, the National Weather Service’s explanation of dew point and condensation shows why those day-night swings matter. Add limited airflow (everything closed), a coastal or humid climate, or tiny leaks around windows and hatches, and you’ve created a perfect environment for mildew.

Start with your storage reality: temperature, power, and access

Before you pick a device, answer three questions:
1) Will it freeze where your RV is stored? If yes, avoid draining a dehumidifier into your plumbing; standing water can refreeze and crack traps or lines. Prefer a removable tank or passive moisture absorbers.
2) Do you have power? No outlet means no electric model; use desiccant tubs or bags. With power, choose a unit rated for cold conditions.
3) Can you check the RV during storage? If it’s parked at home, emptying a tank weekly is easy. If it’s off-site or you won’t visit for months, go passive and set multiple absorbers.

Which tool works best in winter?

Compressor (refrigerant) dehumidifiers are the “household” style. They excel in warm, humid air but struggle near or below ~40°F; coils ice up and performance tanks. They’re great for heated indoor storage with regular check-ins, but they’re usually not the best choice for unheated winter conditions. ENERGY STAR’s guidance on choosing dehumidifiers is helpful when comparing capacity and efficiency.
Electric desiccant (heated-rotor) dehumidifiers use a moisture-absorbing wheel and gentle heat, so they keep working in colder air. If you have power and can empty a small tank periodically, they’re our favorite for cold garages, carports, and covered storage.
Chemical desiccants (calcium-chloride tubs or silica-gel bags) require no power, make no noise, and won’t freeze. They’re ideal for fully unattended storage. Place several in moisture-prone zones (bathroom, kitchen, under-bed compartments, wardrobe). Set each tub in a shallow tray for insurance against spills.

When you definitely need an RV dehumidifier in winter storage

• Humid climates: Coastal regions or southern winters still carry plenty of moisture.
• Frequent daytime warm-ups: If afternoons climb above freezing after cold nights, condensation cycles intensify.
• Stored soft goods: Bedding, mattresses, and cushions retain moisture; the more fabric you leave inside, the more dehumidification helps.
• Limited ventilation: If you can’t safely crack a vent with a cover, mechanical or chemical moisture control becomes more important.

Sizing and placement (so it actually works)

If you choose a powered unit, match capacity to your rig’s size. Manufacturers list “pints per day” and recommended square footage—err on the larger side for fifth-wheels and Class A’s. Center the unit where air can circulate (galley or main aisle), keep interior doors, wardrobe panels, and drawers open for airflow, and elevate mattresses slightly with breathable spacers so air reaches underneath. For passive tubs or bags, go for coverage over concentration: a few smaller containers placed in bathroom, bedroom storage, and the galley often outperform one giant tub in the hallway.

A smarter hybrid strategy

Most of our guests skip “one device to rule them all” and use layers: a small electric desiccant unit (if powered) plus multiple passive absorbers tucked into dead-air zones. Add a vent cover so you can crack one roof vent safely, and you’ve set a slow, steady path for moisture to leave rather than re-condense. The U.S. EPA’s overview of indoor moisture and relative humidity reinforces the target range—aim for about 40–50% RH in storage to curb mold and protect materials.

What about low-humidity states?

If you store in truly arid regions and your rig sits under a well-ventilated cover, you may get by with airflow and a couple of desiccant tubs. But “dry climate” is not a guarantee; sealed interiors still trap moisture from soft goods and day-night swings. A $10 hygrometer tells the truth. If you see readings above ~55% for days at a time, step up your moisture control.

The safest cold-weather setups

• Unpowered, unattended, and freezing: Multiple calcium-chloride tubs or high-capacity hanging desiccants throughout the rig; crack a vent under a cover if possible.
• Powered and freezing: Electric desiccant dehumidifier with a removable tank plus a few passive tubs in storage bays and the wardrobe; check weekly or bi-weekly.
• Heated indoor storage: Compressor unit sized for your RV, hose-drained to a bucket you can empty often—or set a timer so it doesn’t run nonstop.

Simple habits that prevent springtime mustiness

• Deep clean and dry: Wipe hard surfaces, shampoo spots if needed, and let everything dry thoroughly before closing up.
• Empty and prop the fridge/freezer: Leave doors ajar with a box of baking soda inside.
• Encourage airflow: Open interior doors, lift cushions and mattresses on spacers, and pop wardrobe panels.
• Use a hygrometer: Small and cheap, it’s the best early-warning system.
• Check seals now, not later: Replace tired window and hatch seals; tiny leaks become big moisture problems in storage.
• Document and distribute: Snap a few photos of where you placed absorbers and devices so you can check or replace them quickly mid-winter.

Safety notes you should actually read

If you run any powered unit, secure cords off the floor, keep the device flat, and never drain into winterized plumbing. Empty tanks before they’re full so the unit doesn’t shut off for weeks. For chemical absorbers, tray every tub and keep them upright in travel; calcium chloride turns to brine as it works. If you’re sensitive to indoor air quality, remember that your goal is stable humidity, not zero. The EPA and building-science community consistently recommend maintaining healthy humidity levels rather than over-drying interiors.

Common mistakes we see (and how to avoid them)

• Using a compressor unit in an unheated barn: It will ice up and stop dehumidifying—use an electric desiccant instead.
• One giant tub in the kitchen, nowhere else: Spread smaller absorbers across closed compartments and the bedroom.
• Closing everything airtight with wet textiles inside: Dry bedding thoroughly or store it at home.
• Forgetting to open interior pathways: Closed closets and drawers trap humid air.
• No vent cover: Without a cover, most folks keep vents sealed—and moisture sealed with them.

A note on product lifespan and expectations

Some compact dehumidifiers aren’t built for years of continuous use. If you buy a small unit, treat it like a seasonal tool and store it indoors between uses. Desiccant tubs and bags are consumables; plan to replace them every 30–60 days depending on climate and RV size. Keep a simple log taped inside a cabinet: date placed, locations, and replacement dates. It takes 60 seconds now and saves you guesswork later.

What we’ve learned from hundreds of winter layups

The rigs that open fresh in spring almost always follow the same pattern: a realistic plan for the climate, a right-sized device (or passive coverage) for the RV, interior pathways opened for air, and a quick mid-season check. The rigs that open musty usually relied on a compressor dehumidifier in the cold, used one lonely absorber, or locked humidity inside soft goods.

The bottom line from our campground team

Choosing an RV dehumidifier in winter storage isn’t about brand loyalty; it’s about matching your storage conditions to the right moisture-control strategy and giving humidity a way out. In mild, powered settings, a small electric desiccant unit plus a couple of tubs works wonders. In unpowered or fully unattended scenarios, a network of calcium-chloride tubs and vented airflow is simple and reliable. And in heated indoor storage, a properly sized compressor unit shines. If you keep your RV between roughly 40–50% RH, you’ll protect fabrics, woodwork, electronics, and your nose when spring arrives.

Ready to build your plan? Bring your storage details to the office at check-in and we’ll help you choose the best RV dehumidifier in winter storage setup for your rig—so you roll into spring with a clean, dry RV that’s ready for your next adventure.

Author: Ric Favors