Why not crank the engine and blast the heater a few times during the night?
Although inconvenient and not conducive to a very restful sleep, it should
take the chill out for a while.  Of course, cracking a window or 2 would be
a good idea in case of exhaust leaks... However, I am of the mind that a
decent sleeping bag and flannel jammers are the way to go.

Peter 85 Westy GL "Nesta"
Willard, WA