I've got a 2015 Voltage 3818. 18" garage, I did give up the loft and second bathroom for the garage space, however going to this size garage did give me 3 happi jack beds that drop down in the garage. I can get two polaris RZR's in the garage or a quad and an RZR with plenty of room to drop a bed with the bikes in the garage during quick road travels for the kids. Mine has the "artic package" as stated it's just a cover over the bottom of the rig and a heat duct that blows a bit of heat in it.. It does make a difference but it's not really built for heavy winter camping. My rig is heavy, when fully loaded up at 20k my 2013 6.7L knows its there. I've owned the all the ford diesels starting with the old 6.9L, if your patient and not in a hurry the 7.3L you have will get you where you want to go but not in any type of record time.
I have done some "cool" weather camping in it (lows in the upper teens) and I'd have to say it just depends on what you have going on. If you are boondocking you will go through the propane like crazy, if you are able to plug in get two of the infrared heaters (one in the kitchen, one in the garage) and supplement with the furnace and it's very doable.