Dave, we were at Palo Duro State Park (north TX around Amarillo) this past December where it was in the high 20's at night but quite comfortable during the day. The propane
regulator went out somewhere between NC and TX so we just had the heat strips in the AC unit for a couple of days but that worked fine for us. From there, we went down to Big Bend National Park and the temps were even better - 40's at night and low 80's during the days. Not sure how the kids would like these Parks as there's no 'canned' entertainment but we had a ball.