[gumby79]

I considered a similer thing(trailer heat) with my 5th wheel .
I thought simpler and easier than exhaust , engine coolent. Less chance of stoping to find my cats and dog CO2ed after 12+hrs on the road.
Add .5"return and .75"feed pipe (isolated) to the rear bumper use hydraulic quick disconnect(QD), they seal both male and female unlike air QD, and a slinky hose to a set of QD on the trailer , heater core from a 15 passenger van.with a 12v fan blowing into the floor duct for the stock heater. Before someone says ,Why not just use the heater that came with the ducting? This was a transit problem can't use the furnace @55mph ,keeping the water lines and tanks(60ga fresh, 2x20gray, 40 black) from freezing during winter travel over Donner Pass and others below 0f at times. But life changed and I didn't get that far with the idea.
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For exhaust a 2"+ umbilical cord would be needed,and high mounted to give enough slack /flexibility for turning. Do you have a catalytic converter? If so that would be my sorce of heat. 600-800°f a cat starts to work .by the time you got to the trailer it should have cooled sufficiently. Passive or forced air?