Just in case anyone is crazy enough to try this. Here is a great website to help you DIY a heater install. It's actually a computer cooling enthusiast site, but the principles are exactly the same. Instead of robbing heat from a CPU and distributing it to the air, you rob it from your engine's or genset's coolant, or from copper pipe run around the exhaust stack of your diesel, wood, or propane stove and distribute it to the air.
Radiator - Review Tom's Hardware : DIY Water Cooling 101
Basically this is how to build a red-dot heater, or replace one of these (bottom right of the page)
DickinsonMarine.com - Alternative Heating
for a fraction of the cost.