Opening a window or vent an inch or two will help with the dampness. Breathing releases a lot of water vapor into the cabin, and it will condense wherever is finds a cold surface, especially windows
. Pieces of Reflectix (the tin "foolish" stuff with bubbles in the middle) covering the windows
will help a lot- Velcro tabs to hold them in place, perhaps.
Getting something on the walls will help a little, too.
It doesn't take a whole lot of heat to raise the temperature in such a small space. If it doesn't have a furnace
, most people find a small electric heater on low does fine with hookups.
For the future, if you plan to camp a lot in colder temperatures, a furnace
is a good investment. If it's only an occasional thing, it might be better to use a heater and pay for electric.