You are really asking for a lot. Four season living in a fixed spot, you can put in heat lines for your drains and water feed, you can put in skirting to hold in any heat and prevent freeze ups.
But four season travelling is a real different ball game when actually living in a fifth wheel. Purposely travelling to snow country usually involves altitude, and hills. Stopping a heavy fifth wheel on an icy road when the brakes are useless is almost impossible. Keeping water lines open, and furnaces running while on the road can quickly go from lots of fun, to a total frozen broken rig.
There are some expensive units with three inch insulation in the walls.
Tell us what your budget, requirements, temperature range expected, and ability to remain on your own in the event you get snowed in might be.
