I've an E250 I've converted: insulation, fantastic vent, LED's etc., all nice. Where and when I go camping, sometimes a heater would be really nice. I've got a small electric for when I've shore power...
Our 30 ft. Class C came with a catalytic heater installed by previous owner. Pretty nice and unique. It is attached to the wall just inside the door; about 2 ft. by 2 ft. and 3 in. thick. It's hooked into the propane system. Ingnites by spark and operates with no electric at all. Puts out a lot of heat but of course no fan. Great when dry camping.