<<Yes, they're small and all, but when it's 20 below, I'd rather have
heat.

The 16,000 btu Hydroflame in the A'wagen makes camping in sub-zero
temps enjoyable. (If you don't open the door....) I suspect that it
would even keep a Westy toasty.>>

I've only camp down to about 10� here in Alaska, but the Atwood perform admirably. (12K BTU) I don't have pop-top installation, so sleep in the lower quarters at frigid temps with the top down. Stayed very tosty. Be careful about bedding hanging down!  Not sure it would get hot enough to catch fire or not, but the furnace is not necessarily in the most ideal spot for safety.  One of these days I will put a thermal curtain across the front (just behind the seats) and this should help even more to save on propane, and make it easier to heat. Lots of glass and unused space while sleeping that could be isolated from the rest of the van. I also use an "extend a stay" and a separate propane tank.  . BTW, the Atwood's can be had for under $300 on eBay brand new.  I think I paid $279 for mine about 3 years ago. 

Troy