I agree no real way to fix frame rust. But here's another idea. Might be a little long term though.
Jeep Wrangler YJ tub and frame
Or just do a search for Phoenix wrecking yards and buy the back end of a damage jeep frame. Then have that welded on to your frame. Much less fabrications and that means cheaper. Avoid body shops you need a welding shop, much cheaper.
If you have a garage to work in you could do all the removing of parts and frame cutting. Then just get a mobile welder to come to your place to weld it. Then put it back together yourself. But, WI in winter, damn, not a good project this time of year.