My concept is a modular 12 volt heating unit, that can be mounted to the hatch opening in a few minutes (or removed). I’ll run a 12volt 20 amp line with a plug to the hatch area to allow quick, single point connection to my house battery.
I’ll post pics as I go so you guys can enjoy my bizarre thought process.

Template progress pic with a lot of temporary stuff hot glued to it to establish the interior surface and angle of the hatch.

Diesel heater I’ll be using (5kw advertised capacity).