There are many variables in heating a space, any judgement really needs to specify intended volume, hard or soft camper sides, ambient temps, expectations, personal comfort levels. I use a Wave3 in a small insulated-fabric popup (5.5 ft truck bed with overcab), and rarely park in less than 20F, almost always in dry Western US locations. Most of my use is at freezing or 40sF. The heater is located at center floor level, just right when sitting at the table, and between two venting locations.
It works very well for me, raising the camper temp from, say, 40 to 50 in about 15 minutes on high, and to 60 within the hour. The heater itself is robust providing it is maintained correctly: protect from dust (keep cover on when not in use), avoid jarring the thermocouple or other parts, ensure tight gas line connections. The built-in sparker occasionally does not work, but it's very easy to use a match or lighter.