I suppose that depends on the weather, the vehicle and how comfortable the seats are wink I'd like to see how well a mummy bag in a car does compared to a mummy bag in a tent.

Considering that the seat and carpeting are keeping me up off the ground and dry, and that I expend zero energy in building a shelter, I'll continue to plan on using the truck cab as an expedient shelter.
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Better is the Enemy of Good Enough.
Okay, what’s your point??