It's possible. But skirting is a necessity, and likely a small heat source under the trailer in addition to the furnace blowing into the underbelly.
I didn't say it was going to be cheap!
Danforth bay CG in ossipee NH offers winter sites, and while they shut the water off at the pedastle, you can fill your FW tank.
People do it, but it's expensive. Most CGs put you into metered power over the winter.
Propane will be used, of course, but you should seal the windows with that shrink wrap plastic sheeting. The condensation on the inside of the window panes gets extreme without that second "pane."
The heated underbelly only lets you drop to 22 degrees ambient. Below that you'll have dump valve freeze up.
So, skirting made out of the stiff pink insulation board, sealed with tape is your only hope, with a heat source (a couple 100 watt incandescent bulbs for example) is your only hope to emerge in April without problems.
Danforth Bay in Ossipee is where I winter the trailer because we ride snowmobiles right off the campground onto the trail system. The "winter" sites (about 30 of them) are booked solid from November to April. Everyone is there to ride or ski or ice fish.
Well, there were a handful last winter that were there full timing for one reason or another.
Craig Bailey
New Hampshire
Jayflight 32 BHDS
Chevy 2500HD CC