The 'quality' issue has been discussed for years. RV's are just not well made, as a generalization. You'll just have to pick a model that fits your needs/wants and kind of hold your nose.
Everyone has their opinions on what brand is the best, or better quality.
As far as staying warm in a popup, we've had no problem with that. The heater works just fine. If you have electric hookup, you can, of course, get a ceramic heater instead of burning propane.
No longer RV'ing