It can be done, try and learn from others' experiences so you don't have to pay the consequences...
If you end up with a trailer that has an outside shower, I have read that it is easiest to unhook it inside and cap the lines, then insulate the opening really well.
We had not camped in low temps but had the need to this last weekend. They were not brutal temps, but rather in mid 20s at night. It warmed in the daytime to 50+ so was nice. I worried about our Arctic Fox but we had no issues. We had 15amp service available so were able to use furnace without running batteries down. The furnace did run more than I expected, but the north wind probably did not help.. we had to have the vents opened alittle to keep condensation down.
Start your list of must have items and the limits you have (money, weight, etc) and keep looking and researching, you can do it.. keep us informed as you progress.