I use battery warmer for my engine.

Ive been preheating my engine while driving to spots by placing it on the passenger side floor, and turning on the floor heater in my car. But if i spend to long raking/digging/sculpting dirt she goes back to stone cold. Rather than buy an engine heater, Reckon if i hack the parts out of an old electric blanket 'Macgyver Style' could it be rigged onto a car battery? Or wired onto a car cigarette lighter plug. This would be used for remote areas where there's no power point for a heat gun.

....And if i clip my car jumper leads onto a heat guns plug ends, Will i spontaneously combust?

No. Do you not understand the idea of A/C and D/C?

It wont work but you can buy a cigarette lighter plug in that you can run your heat gun off of.