Hi
Not specifically dealing with the windows which Damian has explained, but in general condensation is a common issue in caravans. It's not normally a sign of anything wrong, its a natural consequence of having living breathing bodies inside a confined space, with less than ideal insulation - a caravan.
Typical sources of water vapour are breathing, any open flame (Cooker or oven), and boiling of water, extensive usage of hot water such as a shower.
Large appliances or those used for extended periods such as the fridge, Water & space heaters have by law to be 'room sealed' which means they do duct their products of combustion outside and thus cannot contribute to condensation inside the caravan.
Condensation can become a problem if it doesn't clear easily. By far the best method is ensuring there is good ventilation, especially when the caravan is in storage. Leave cupboards and lockers open to allow free air circulation.
Using dehumidifiers or water crystals to remove condensation may have some benefit for a short while after using the caravan, but long term usage is pointless exercise, and may mask an issue and will certainly cost you for energy or crystal refills.
If you do get signs of continual condensation when in storage, then you should suspect something may have started to go wrong, and its worth arranging to have the caravan surveyed for water ingress.