Prepping the RTT for cold weather

This will be my first winter in a rooftop tent. Trying some ways I used in-ground tents to block some of the cold from coming up through the bottom.
I have to admit I like the RTT a lot more than I thought I would and look forward to some cold weather camping.
What are other options for keeping warm in one of these hard-shell RTT?
A compact diesel heater is on order and should be here in a few days.
Put your suggestions in the comments.

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