If a vehicle is carrying the weight, staying warm in a tent is easy. Until you get out of the sleeping bag!
My formula is 1) cot 2) insulating pad (cheap is ok) 3) Phat sleeping bag. I use the Therma-rest backpacker cot if room is an issue. That thing works. Warning -- put padding under the feet or it will wear a hole in your tent. Given the room, I use a bigger cot. Or preferably my 6-foot Toyota truck bed with a topper
There are many tricks regarding what to wear inside a sleeping bag, but I'll just say it needs to be dry and you need a beanie cap. I also sleep with snacks and a pee bottle within reach. No getting out in the cold to pee for me.
If you want to be warm out of the bag, look at the Little Buddy line of products.
