A true 4 seasons trailer has to be able to survive a 3 day ski outing with the temps below 0F at night and never above freezing. You need heated water tanks, pipe and valves. Extra wall and ceiling insulation are important and and insulated floor is also a must.
Boondocking in winter is out unless you are willing to carry water in jugs and use a portable toilet. For a 3 day weekend I would want at least THREE 20 lb LP battles, maybe FOUR ! You probably won't be able to use your furnace because it will kill your batteries.