Winter camping can mean many things depending on where you are and when:
- Down into the 20-30's, it's a complete non-issue. You can probably get away with blankets and no heat at all in a small truck camper.
- Down into the -10 to -20, it becomes more challenging
Also, do you expect to have electricity? With shore power, you don't have to worry about batteries running out and may even be able to supplement with a space heater. In our 25ft travel trailer a 1500w space heater is all we use down to around 30F. I would expect with a smaller space, you could manage even in colder conditions.
As mentioned, moisture is the biggest challenge (and a good reason to avoid the stove heating among others). The bubble foil insulation on the windows will help a lot. If only doing it for a few days, it's mostly a nuisance, just make sure to wipe down every interior wall you can before closing it up (inside cabinets also), so mold doesn't start growing.