Update: the oil filled radiator is great. unfortunately, the "hammered metal" paint I used never stopped stinking. so I have ordered another for $25 on amazon. one negative is that its a radiant so if u open the camper door and lose ur heat, it takes a while to recover. it also takes a while to warm up the camper. on the plus side, it is silent. thats big.
meanwhile, I bought a small cheapo "comfort zone" ceramic from walmart for $15. it also has issues, noisy, and on hi the thermostat fools itself and it shuts down often. as a plus, the hot air instantly warms the space. and recovers fast from an open door. It runs at 750 and 1500 watts on lo and hi. in my TT, the 750 level is adequate to keep the camper comfortable on a 10 degree night (tonight) so the problem with it early cycling on hi is not an issue. but I dont like the noise.
so i ordered another oil filled and I will not paint this one lol, and keep the ceramic for a backup.
I should add that I have not and dont plan to camp in winter and if I do, there arent many places open with electricity anyway. but doing this exercise is good just in case and cuz its fun.
finally, I looked at VENTED propane heat. I do NOT trust unvented anything
. oxygen sensors help but I just wouldnt be able to sleep. there is a VERY cool marine one called Cozy Cabin. It is vented, and it still has a low oxygen cutoff It's marine so it's stainles and its small with a 1" vent pipe. I have no idea how good it is in practice and they are expensive $500 or so. Also, I read that a 20lb propane tank doesnt like to make gas at very cold temps. I think a blanket may help with that, not sure.https://www.westmarine.com/buy/sig-marine--cozy-cabin-propane-heater--237412