Our vehicles are not 100% rain, dust, ash and sand proof. Motor Homes and Campers are never built to be airtight (breathing holes for electrical and gas equipment). Driving in dusty conditions could cause the vehicle to fill or leave traces of sand, dust or ash. Actually you will notice dust in all vehicles (normal cars as well) when driving on gravel roads. This is pretty common in Iceland.
Due to heavy wind and rainy conditions the vehicle could at some point get wet inside whether it is from condensation or effectively from rain. When entering the vehicle with wet clothes or shoes you will notice moist very fast. We recommend leaving a small gap on the top or side window to allow the moist to exit. Every morning we recommend turing the heating system on full speed and opening a top window. Make sure it does not rain inside the window.
Due to heavy dust, ash and sand (especially on gravel roads) locks can fill up with it and get clocked. We recommend just locking doors that actually allow access to the vehicle.
Remember to close all latches, hatches and windows before driving off.