When I towed I ran the furnace as I wanted to camp as late and early as possible. This was while I lived in WI. There is nothing like parking the trailer and getting out of the cold into a warm trailer. Besides towing with full tanks in a blizzard you need the heat to prevent freezing. I have just installed a new furnace in my MH and I plan on running it while driving as necessary. Of course I am also one of those owners that has run their refer on gas while towing. I undersand the risks of this and take the steps that are necessary when pulling in to fuel and traverse tunnels. Fuling requires shutdown of all gas appliances prior to entering the station lot, and tunnels I turn it off as required by DOT rules.
I figure propane is not any more dangerous than the 50 gallons of gasoline that are in a tank that has no protective rail mounted outside of the frame rail. I have a 76, built prior to the 20/20 expose' on GM trucks. It is on my list to do, but has not yet risen to the top. Just my $.02 worth.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato