Welcome to the forum. Great question and one that many of us have had experience with.
You will have condensation in the trailer if it is open or closed. The issue is a few days of warm (relatively) humid air followed by a cold night. There are several solutions depending on how severe the problem. You can try the solid dehumidifiers such as damp rid. If they are not enough, you can also try the solid state (pelletier) and finally a small compressor type dehumidifier. You will need power for the last two. The solid state ones are not very effective as they move a small amount of air and can only remove a limited amount of water. The household types are more effective, but take up space, and need to be emptied periodically if not connected to permanent drain. Neither works well once temp is below 40F. I used a solid state model in my PUP years ago, but have a 30Pint household unit in my current TT. It is on a separate power source from house and permanent drain, I shut it off at main (house) breaker when ,40F).
if you have any mold starting, open unit and all windows on a cold dry day and air good. Also wipe mold with the disinfectant product of your choice.
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