One non-ducted furnace enough?

I've seen many comments that TM's are toasty warm even in cold weather.

My wife was concerned that the used unit we are looking at had one only, non ducted "pop up"type furnace.

We do a lot of early spring and late fall camping in ND and nights can get cold.

Does one have to run the furnace most all night in cold weather to keep warm or does the TM's insulation mean it stays pretty warm?

I do keep several spots open to the outside a crack all night for ventilation/condensation purposes.