[dingov70]

I have installed several air heaters & would not recommend fitting one into the boot of your car.
Reasons ? fuel supply / heater cold air supply / piping for heated air / heater exhaust outlet / the list goes on

It is far simpler to install a water heater system & 12V coolant pump to warm engine / coolant

12V diesel heaters are available , but many have been run without servicing & become costly to put right .

When I installed air heaters , they were into vans with truck mount cleaning machines . The heater was mounted under the van & the heated air trunked into the front of the van load space at floor level & drawn out by the rear door via a snorkel to create air flow with no cold spots .