road pro. at most truck stops they are 300 watts heat my 4 x 9 teardrop rather well with 2 inch insulation in the walls. they are battery hogs I run mine for like 15 mins after I shut my car off. and they will heat pretty good for pre heating before bed time 15 mins to 30 with the car runnin while cooking dinner than shut car off for 15. that's good enough for windriver rocky moutains in Wyoming with maybe frost on the ground in august. ah. I also run a northern 12 volt blanket inside a army sleeping bag or a set of 2 quilts...........they run on a timer all night another top notch item. still go 50 percent on the battery by moring than I recharge from the car while I eat breakfast or break camp and drive. I can charge my battery while towing. I don't use solar or generators.
have heated with 12 volt for like 5 years.
also the dash heaters from Walmart junk got to pay 39 dollars at your truck stops on the interstate or go to ebay road pro sells top notch good 12 volt pruducts.
and 300 watts of heat beats a barely 100 watt on a wallmart el cheapo dash heater.
got to buy the good stuff on 12 volt heaters.
slow. it wont run you out but it will take the cold of nicely lots of insulation in the walls and good blankets and they work nicely.
Plans. there was supposed to be plans to be followed when I built this thing. Opps! AH, gee, tum,tee tum. I think I forgot about the plans 2 years ago. ------Tow vehicles, 1995 ford explore, 1994 ford ranger, 1993 ford F-150, 2009 4x9 Off road teardrop, on harbor freight greatly modified frame.