Unfortunately  condensation is likely to occur in most  caravans simply  because one side gets hotter than the other  when the sun shines on it,  and whilst in storage in  cooler months that  can trigger some condensation, BUT as the sun moves round,  so will the condensation,  and ultimately  there is no moisture gained or lost compared to the ambient  humidity levels so its a status quo.
Removing  soft  furnishings and as others have said keeping  internal doors and cupboards open enough to ventilate the difficult  spaces should be all that's needed.
There is a limited use for dehumidifiers. When you  use a caravan the levels of absorbed moisture in the furnishings and some wood may rise,  simply because we breathe out  quite a lot of water vapour, and when you cook,  often you might boil water which of course produces water vapour,  and whenever you use an open gas flame such as on a cooker or oven, that also produces water vapour (your gas water and space heater have room sealed combustion so they  do not add any water vapour to the living space)  after a few days of occupancy, the moisture content will have risen a little,  so  when you first put the caravan into storage,  having  a moisture trap will help reduce the excess moisture,  but  beyond the first  few days it  will make no  difference to the caravan as the essential ventilation will just  keep replenishing the extracted water.
If you do have a damp problem,  then rather than treating the symptom  which might  allow the problem to get worse and cause serious damage, its far  better to correct the fault.