Hello ttfn,
You are into a losing battle if you are trying to keep moisture at bay in a caravan in storage.
Ventilation Ventilation Ventilation is the way to go.
The causes of condensation basically the fact that warm air can carry more moisture than cold air. So you get condensation when warm moist air comes into contact with a cooler mass, such as metal fittings or cold plastics. This drops the temperature of the air in contact with it, and as the air cools any moisture excess to the dew point of the cold air has to be re condensed and forms condensation.
A caravan in storage will be subject the heating effect of the sun, which warms the air inside. This makes the air hungry to grab moisture, but then when the sun goes in, the skin of the caravan cools, and the edges of the warm body of air in contact with the walls and windows cools down, drops its moisture, and also the cool air drops to floor which sets up a gentle but persistent convection cycle and brings more of the moist to the edges of the caravan, dropping more condensation.
The other effect of continual heating and cooling is the warm air tries to take up a greater volume, (that how hot air balloons work) and as the construction of a caravan has fixed dimensions, the extra volume of air will find its way outside through small gaps in the construction and fittings. Being warmer it will quickly dissipate outside. But when the caravan cools the internal mass of air will contract, and that will suck new external air into the caravan through the same cracks.
Even if you cover all the ventilation holes, there are still plenty of ways that air exchange can take place with the outside, gaps sealing around the fridge and other equipment, gaps in doors & window seals.
You can't really stop this happening, which renders dehumidifiers ineffective for long term storage.
It is better to encourage free air exchange with the outside. This allows any heated air to escape readily which helps to keep the extremes of solar gain temperature down, and when the moisture content of the caravan matches the air no extra moisture can or will be deposited.
The only times a dehumidifier has any practical benefit, is if the caravan is in use, where warm bodies exhale high moisture content in their breath, and open gas flames such as the cooker add moisture to the air, along with boiling water in the kettle or cooking pans. When in use at elevated temperatures above ambient the fabrics of the caravan will have a raised moisture content. A dehumidifier may help to bring it down, but by far the best way is ventilation. The other time a dehumidifier has a benefit is when you have just finished a holiday, and for the reasons above the fabrics are moisture laden, so for a few days after a trip a DH will help to remove excess moisture.
If you have a damp problem because of water ingress, then no amount of dehumidification will be as beneficial as getting the source of the water leak sorted out.
If you are concerned about wildlife, rather than covering the vents completely, get some fine expanded metal mesh and create internal domes so that the surface area of the dome provides about the same open surface area as the underlying vent hole.
Good luck
Facebook
Twitter