Up here it's common amongst construction workers on remote or out of town sites to live in 'bunkies'. They are almost always built on the frame of a junked TT but sometimes on a car trailer or other repurposed trailer.
They are stick built with 2" x 4" lumber (with lots of wind bracing LOL) and plywood with spray foam insulation and residential windows. They are built with all the plumbing on the warm side and ample heating. Some are heated with propane, some with electricity. Usually they are clad with agricultural style metal roofing and siding with extra screws and trim to make them transportable without issue.
Most of them are pretty austere but I know of several with big screen tv's and lots of luxury too. It's really not difficult to fit everything you need into an 8' x 20' or 25' unit if you stick with the basics and pass on space-wasters like dinettes and use an E-W bed or Murphy Bed.
If you're handy they are also a LOT less expensive than a standard RV is.
I know several guys who live in them year-round without any problem or discomfort at all.