Hi Naio,
Condensation happens when the surface of the material is below the dew point temperature. Two solutions may be used together to help ameliorate this issue. Raise the surface temperature of the material and/or lower the relative humidity inside the RV.
Leave the cabinet doors open.
Radiant heaters warm the surface they are pointed at so they may help the surface to get higher than the dew point.
If you have shore power, then try placing a "trouble" lamp with a 60 watt bulb at the bottom of a cabinet against the exterior wall. Be careful to leave an air gap--you don't wish to burn the RV cabinet. If that solves the issue, then add other similar lamps.
If you are NOT on shore power then place a 12 volt fan blowing air into the bottom of the cabinet. Use the lowest speed that solves the issue. If it works on one cabinet--add additional fans.
For window condensation, place a 3 inch wide strip of insulation on the outside bottom of the window. The condensate will flow down the window until it hits the warmer glass and then return to the air inside the RV.
Do not use an unvented blue flame or catalytic heater. They add a huge amount of water vapor.
Cracking a roof vent and opening the window farthest away from the vent may help. If an electric heater is placed at the open part of the window it helps even more.
I found that running an electric heater, and the roof air conditioner at the same time would drop the relative humidity dramatically--which lowers the dew point temperature. This "forces" the roof air conditioner to become more of a dehumidifier. Obviously this requires a lot of power. Be sure to monitor voltage and if it drops below 107 do not run the roof air. I found that in extreme cold the air conditioner fans did not wish to operate, but at those temperatures the relative humidity is so low that dew point issues are not much of a problem.
Another shore power solution is to use a dehumidifier. They work better the higher the temperature is inside the RV.
I hope this helps.
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.