I just put a space heater in my car, leave it on and plugged into a receptacle that has an indoor switch. Leave the switch off until needed. It could be out on a timer.
1984 chevy suburban, custom made 6.5L diesel turbocharged with a Garrett T76 and Holset HE351VE, 22:1 compression 13psi of intercooled boost.
1989 firebird mostly stock. Aside from the 6-speed manual trans, C5 front brakes, 4th Gen disc brake fbody rear end.