Having "wintered over" twice in Montana, once in a Class A and once in a fifth wheel, I can say from experience that there are NO "must haves"!
However, there ARE some things that are "good ideas".
In a Class A (and, to a certain extent, in a fifth wheel), skirting is a good idea. I used Reflectix aluminized bubble wrap insulation to skirt the Class A, plus I covered the grill and windshield. It turned out to be a VERY good idea!
It is also a good idea to get a large propane cylinder or tank. I used a 100 lb. cylinder for the Class A, and leased an 80 gallon tank for the fifth wheel. Of course, the 100 lb. cylinder is more portable, but hauling it to be filled was a pain!
I found that making the water line out of hard copper tubing was another good idea, then installing heat tapes and wrapping it with pipe insulation eliminated freezing problems.
Apparently, the hot water running through the sewer lines prevented freezing, and/or the snow insulated it adequately. We never had a freeze problem there, either.
When we encountered a cold draft, we hung a blanket from the Thrift Store over it. that worked.
While we had an electric heater, we rarely used it.
"Wintering over" requires planning and thought and common sense.
Yes, it CAN be done, HAS been done, and WILL BE done again by somebody.
Good luck.
CM1, USN (RET)
2017 Jayco TT
Daily Driver: '14 Subaru Outback
1998 Dodge QC LWB, Cummins, 5 speed, 4X2
2 Kawasaki Brute Force 750 ATVs.
Pride Raptor 3 wheeled off-road capable mobility scooter
"When seconds count, help is only minutes away!"