I'm a 3 season camper (Fall/Winter/Spring) with the Tepui version of your Mt. Shasta Summit Series. I've tried the Mr. Buddy propane heater in the tent, but it produced too much moisture while running, causing condensation on the tent walls and damp/wet bedding. In colder temps, we had thick layer of frost build up on the tent walls and aluminum supports, which turns to water when the sun rises.
Now, it's Smartwool or polypro long johns, Smartwool Expedition socks, heavy wool blankets, a wool neck gaiter and watch cap. Fill a pair of Nalgene water bottles with boiling water a half hour before bed and a
candle heater for tent(goes between mattress and blankets, one at my feet and one near my kidneys). Pull on a pair of loose wool mittens when I climb into bed and I'm good for the night unless more than a few hours below 15-20°. A cheap chemical heat pack in each sock/mitten will get me down t0 single digits, although not comfortably.