The first thing to say is most folding campers, most trailer tents and even some caravans can suffer from this at times,its most directly related to the out side temperature,when the evenings cool down and the underneath of the bed boards get cold, the heat from your body reaches the top of the bed board, hot meeting cold so often leads to condensation.
There may be a few ways to cure it but most will entail stopping your body heat reaching the bed board,we achieved this by using self inflating air beds on top of the mattress,if you dont know what these are you can forget the normal camping air bed that you need to inflate,these are normally about 50mm thick and have a foam filling,you do not inflate them opening the valves allows the foam to fill with air.When packing away open the valves roll the air out and close the valves,its that simple.
Before using these we tried insulating under the mattress but found it just moved the condensation to the top of the insulation,if you are unlucky enough to get this you must prop the mattress up during the day to allow it to dry.
There may be a few ways to cure it but most will entail stopping your body heat reaching the bed board,we achieved this by using self inflating air beds on top of the mattress,if you dont know what these are you can forget the normal camping air bed that you need to inflate,these are normally about 50mm thick and have a foam filling,you do not inflate them opening the valves allows the foam to fill with air.When packing away open the valves roll the air out and close the valves,its that simple.
Before using these we tried insulating under the mattress but found it just moved the condensation to the top of the insulation,if you are unlucky enough to get this you must prop the mattress up during the day to allow it to dry.