As long as have enough propane and electricity, the furnace will keep you warm. Not all popup TCs are the same, so there is no telling how warm exactly. Our Outfitter was specified at 65 inside with -25 Outside, I think. We only used it in slightly below freezing weather, and that was no problem at all. With the limiting factor being electricity. One battery, one night, as the old saying goes... And solar may not be very effective in winter, with short, dull days and a possible snow cover.
Condensation is always something you need to take into account. Again, not all popups are the same, but keeping a decent ventilation going is never a bad idea.
Just keep in mind that popup TCs tend to be smallish, so it can be somewhat uncomfortable if you need to spend a lot of time inside due to weather.
It is absolutely possible to winter camp in a popup TC, and many people do so successfully. But only you can know if it will work for your use case.
