Personaly I dont have one either. I have an Otter(green)it collects sun heat great when the sun is out. The way I look at it is that I can get about 20hrs out of a 20# tank at $17-$20 per fill. I assume the thermal cap does save some heat but I’m guessing with the price differance of the thermal vs non thermal you would never see a payoff in saving fuel.
Like I said these are just my thoughts with out using one and not buying one. Also i assume there would be some weight difference and im sure the mice would like the extra insulation to make nests with . Im sure some might like it but i can not justify it. -Mark