Any suggestions for keeping warm in a tent?

I think you are crazy but then again I don't like camping in the first place lol.

I would suggest that you want to make sure that you have good quality sleeping bags, have something for on the ground under the sleeping bags to prevent rising cold from the earth.

Best suggestions I can offer sorry, thinking back to my childhood when I was silly enough to go tenting in the winter back home. Also thermal underwear were a god save as it didn't make how cold it got you are always toasty warm on your skin.