I've had the 850w al tank Kat's heater in place for 10 days now, I just wired a mre permanent 110v cord into the interior. I wired them into one common plug that stows in the grill for convieience. I'm really happy with this system, it was 28deg. F a couple mornings.When I climbed into the car, inside was toasty-warm, the windows were frost-free, no need to warm the engine since the gage was registering partially warm already.
Hit the starter, let it run for 30 seconds, start driving
