My RV & Car Dehumidifier Plan: How I Beat Condensation and Mildew

Condensation soaked my camper more than any storm—until I managed moisture, air, and heat together.

Use a dehumidifier for RV to keep 45–55% RH, remove 0.5–10 L/day moisture, and stop window fogging. Choose 150–250 W units with auto-defrost, 35–45 dB, and continuous drain for condensation prevention. Pair with airflow and cleaning for effective mildew control. Monitor with a hygrometer and ventilate during cooking.

RV/Car Dehumidifying — Key Stats & Targets

Source: epa.gov

🧭 Why My RV Gets Wet: Simple Condensation 101

What really causes the fog

I learned the hard way that cooking, sleeping, and drying wet jackets load a tiny cabin with water. Cold glass is the first to sweat, then bedding and lockers follow. When surfaces dip below the dew point, moisture shows up as droplets, musty smells, and—if ignored—mildew in seams.

Dew point in plain words

Warm air holds more moisture. When that air meets a cold wall, it cools, loses capacity, and dumps water on the nearest surface. My fix wasn’t magic: reduce moisture, warm the cold bits a touch, and keep air moving. A dehumidifier makes that cycle predictable, not guesswork.

“Physics doesn’t negotiate; keep surfaces above dew point or remove vapor,” — Dr. Karen Li, ASHRAE Member.

⚡ My Quick Fix Checklist Before I Even Plug In

Vent first

Before switching on anything, I crack a roof vent or a window. Steam from the kettle and damp boots exits fast when there’s a pressure path. In rain, I still vent—just smaller gaps. That single habit halved the time I needed the dehumidifier to hit my 50% RH target.

Heat the cold spots

A gentle heat source lifts surface temperature and stops instant fog. I point airflow at glass and metal frames and wipe visible droplets. A cheap hygrometer on the galley tells me if I’m trending right. If RH stalls above 60%, I bring in the dehumidifier.

“Vent first, then dry—order matters,” — Mike Torres, CIE (Certified Indoor Environmentalist).

🧩 How I Choose a Dehumidifier for My RV/Car

Compressor vs desiccant vs Peltier vs packs

In mild to warm weather, my compact compressor unit is efficient and quiet. In cold weather trips, desiccant wins—it stays effective below ~10 °C and lightly warms the cabin. Peltier “mini” units help tiny spaces but are slow. Passive moisture packs are fine for storage, not wet weekends.

Size and power that actually match the job

I size by trip style: two sleepers, coastal air, and cooking demand more capacity. For a 6–7 m caravan, I aim at 6–12 L/day. Power-wise, 150–250 W is workable on shore power or a small inverter generator. Off-grid, I combine daytime solar with night timer cycles.

Features I insist on

Auto-defrost, continuous drain, tip-safe design, washable filter, and a low-noise mode. A proper hose barb beats flimsy adapters, and a stable base saves headaches when I’m on chocks. I want set-and-forget RH control and a memory restart after power blips.

“Match technology to temperature; desiccant in cold, compressor in mild,” — Sarah Brooks, RVIA Master Tech.

📍 Where I Put It, How I Drain It, How I Power It

Placement

I keep intake and exhaust clear and avoid shoving the unit into a dead corner. I target the foggiest zone—front glass or the wardrobe run—and leave a fist-width gap around the case. Air needs a loop to pull moisture from soft furnishings.

Draining without drama

Continuous drain changed everything. I route a hose to the shower pan or a floor grommet. Short, downward-sloping runs avoid backflow. If I must lift, I use a small condensate pump. I secure the hose so it doesn’t kink mid-drive, and I cap it for travel days.

Power & safety

I plug into an RCD-protected outlet and strap the unit for movement. If I’m on inverter, I check surge watts and cable rating. Timers stop overnight over-drying and save battery. For travel, I empty tanks and latch the float—no surprises at the next campsite.

“Drain path and electrical protection are non-negotiable,” — Rex Palmer, NZ Registered Electrician.

🚗 My Car Setup: Daily Driver to Weekend Sleeper

Fog control on weekdays

For the car, I rely on the A/C’s dry mode first, then a compact desiccant canister near the windscreen. After beach days, I crack windows in the garage and run a small fan for ten minutes. Rubber mats dry faster than carpet—simple swap, less smell.

Overnighting in the SUV

When I camp in the back, I use a low-draw desiccant unit, plus a micro-vent window gap with a bug screen. I store wet gear in a sealed box. Morning glass wipe plus five minutes of airflow resets the cabin with almost no battery anxiety.

“Cars need quick moisture exits more than big machines,” — Ava Stone, ME, Automotive HVAC Engineer.

🧽 Maintenance That Actually Stops Mildew Long-Term

Filters, coils, and hoses

I rinse filters monthly, then check coils for fluff. A dusty coil kills performance and invites smell. I flush drain hoses with warm water and a tiny splash of mild disinfectant, then air-dry them. Before storage, I run the unit in fan-only for ten minutes.

Soft goods and hidden cavities

I lift mattresses weekly and open lockers after rainy trips. Desiccant pouches ride in dead corners: under the bed board, behind the fridge cabinet, near the step well. If a cupboard ever smells sweet-musty, I empty it, wipe with mild cleaner, and dry it with directed airflow.

“Clean + dry + airflow beats chemicals alone,” — Dr. Laila Nordin, CMI (Certified Microbial Investigator).

🔊 Power, Costs, and Noise: My Realistic Expectations

Energy math I can live with

At 200 W for 6 hours, I’m at 1.2 kWh—easy on shore power, planned on solar/inverter. I set a 50% RH target and a night mode. If the kettle and showers spike RH, I run a 30-minute boost, then drop back to silent.

Keeping it quiet

I sit the unit on rubber feet and keep it off resonant panels. Cloth-lined storage bins reduce echo near the dinette. If a fan hums, I clean it—dust sounds louder than watts. I’d rather cycle smart than run flat out all night.

“Control duty cycle; don’t chase zero humidity,” — Prof. Lina Chen, CEng, Building Services.

🧠 My Expert Roundup: What the Pros Keep Telling Me

Patterns I trust

Indoor air pros keep circling the same trio: ventilation, dehumidification, and gentle heat. Technicians care most about drain routing and cable safety. Microbial specialists remind me that cleanliness makes RH targets stick. When I follow all three, mildew stops being a mystery.

“Moisture control is a system, not a gadget,” — Harold Quinn, PE, Building Scientist.

📊 Case Study — My Customer “Sam’s 7 m Camper”

Weekend coastal trips, soaked windows by sunrise, musty cupboards by week two. I installed an 8 L/day desiccant unit, continuous drain to the shower pan, RH set to 50%, and a five-minute vent burst after cooking. The cabin felt drier on day one; the smell vanished by day four.

“Measure before and after; proof beats vibes,” — Nadia Ruiz, CIE, Indoor Air Consultant.

❓ FAQs

What size dehumidifier for a 6–7 m caravan?
I start at 6–12 L/day, desiccant in cold trips, compressor in mild weather.

Is desiccant better in winter?
Yes—more effective at low temps and adds gentle warmth.

Can I run it overnight while sleeping?
Yes, if it’s stable, drained, and on a protected outlet with a safe air path.

Will it drain my battery off-grid?
Plan duty cycles; use solar daytime and timers at night.

Do moisture tubs help?
For storage and cars, yes; for wet weekends, not enough alone.

“Right tool, right duration—context decides,” — Gareth O’Neil, RV Technician (RVDA).

✅ Takeaways

• I keep RH at 45–55%, vent first, then dry.

• I choose desiccant for cold trips, compressor for mild weather.

• I use continuous drain, safe power, and smart placement.

• I clean filters, flush hoses, and air soft goods.

• I cycle energy with timers, not guesswork.

“Simplicity wins when it’s repeatable,” — Dr. Priya Menon, PhD, Building Physics.