We camped many, many long weekends with our 2007 Arctic Fox 990 in high teens to high 20s F without any problems. The one mod we had to make was adding a 2” thick rigid foam sheet of insulation under the mattress. Condensation was a problem with the single pane windows and we had to make sure the weep holes were kept clear and crack open a window to lessen the condensation. We’d stay comfortable inside wearing a few more layers than we would at home, but the extra clothing helped the two 30# propane tanks last longer. Only once did we have a problem with a propane tank freezing up.
We now have a 2017 Arctic Fox 1150 which is the same model only two feet longer and now made with a barreled ceiling four inches taller in the center. Also, this time we added the double pane windows having enjoyed them so much in a 5th wheel because of their sound deadening and no condensation. So far, I’ve only had two nights in the very low 20 F and on both nights I had trouble with the propane tanks freezing up and condensation on the windows. I think considering the small space of a truck camper, condensation is a lot harder to control without cracking open a window than in a larger RV. I’m not sure why I was having trouble this time with the propane freezing up. I think it was due to a less than full primary tank to begin with and not turning on the heat until the interior temp was already in the mid-20s F. We have camped a number of times in the low 30s F and noticed the insulating effect of the double pane windows. They also keep it much quieter on the inside when at truck stops, camp grounds, etc where it can get pretty noisy if you’re trying to rest or sleep.
Good luck with your search and your dreams!