Newbie: Winter Wisconsin camping without Polar/Arctic/etc

We camped at a place a few winters back using a popup. The propane heater with a 20 pound tank kept the tent camper at about 68 degrees for two days. No water but we did have electric. Temps dipped into the twenties and high teens. It was fine for a weekend. I wouldn't want to do much more than that. Good sleeping bags helped fend off the cold as well.