Just chiming in here with my own experiences...
I recently got my '96 4runner. I live in Colorado but flew to Florida to buy it. I researched it and saw that it had spent about 10yrs in the northeast. That immediately made me worried but I had the owner send me as many pictures as I needed, and it was exactly what I wanted so I took the risk. I flew out, went to pick it up, and realized it had a little bit more rust than I thought. 4 spots on the roof would need to be patched and the rear bumper was rusting out. I looked underneath and there wasnt any serious structural rust from what I could see, it actually looked pretty good.
Fast forward to now, 3mo later....
I have since repaired the 4 holes in the roof, putting in new panels, treated it, sealed off any leaks from the top, then headed underneath and treated the rust on the underbody. I am 100% confident that from this point on , I will NOT have any rust issues. I have saved this truck from a downward spiral and will no doubt last as long as I want it to last. Rust was my #1 concern buying this truck and I took the risk, did the work, and now have nothing to worry about. This is on top of all the regular maintenance I have done to it as well (belt, oil, plugs, LBJs, steering components, etc etc etc).
Rust prevention has always been my main concern on every offroad truck I buy. Did it with my jeeps, did it on the 4R, and will do it on all my future trucks as well. Every truck I buy usually has some kind of neglect since I like great deals,end up chopping them up anyways and love to build my offroad trucks up as much as possible. No reason to buy an immaculate 4R or Jeep just to cut the truck up and hack into it.
What it comes down to is responsibility. I dont expect any used vehicle I buy to miraculously fix itself so you have to do due diligence inspecting it, and maintaining it. If it fails, theres nobody to blame but yourself for either not inspecting it well enough, or not maintaining it well enough. We are all capable of doing the work needed to make our trucks last for years and years. If you dont want to do this, then buy new.