Brands that are well built for winter??

Arctic Foxes don't cost over $100K, I think that number is wrong. And note I said to check online to see if four season claims are hogwash or not for a particular manufacturer.

Four seasons where?

Having just wintered in a Rockwood, even though you didn't identify where, should have given you a good idea of what to look for.
If your in an area with nighttime lows around freezing, something like your Rockwood can manage. Enclosed underbelly, heated tank pads, will make it tolerable. As your lows go cooler so does the difficulty. Dual pane windows, additional insulation packages, underpinning or skirting all can help. Most folks take advantage of the portability and just move to suitable climes.

If the fit and finish of the Rockwood are in line with your desires, look at the Cougar and Montana high country lines from Keystone. They dont void a warranty for full timing. Neither does K-Z or Palomino.
Others are available in all the manufacturers lines, find a floorplan you like, then start perusing brands and manufacturers, they all basically make similar designs in their individual product lines.

The term "4 season" means nothing. There is no industry standard for this. It can be nothing more than some hype and a decal. Depends on how much winter you want to tolerate. At a minimum you will want dual pane windows and high insulation values. A true 4 season unit will sell for over 100K and will have thicker walls like a New Horizon, Mobile Suite or others like that.

B.O.

Made by Northwood MFG. in La Grande, Oregon--Arctic Fox and Nash. 4 seasons and well built campers.

Arctic Fox is one there are others. Look for 4 season RV's and then check online to see if they are lying