Let’s talk about rust and taking care of older vans...

I’m looking to build out a camper van, and need to have a 4x4 for snow and sand. I’m trying to stay under 13k for the van itself, and have found a handful of good options - the thing is, they’re all older (pre 2000) and have rust on the rockers, frame, leaf springs, or body. I haven’t driven a car older than 1999, and it was in great condition anyway - so my experience with rust and older cars is non-existent.

What kind of rust can a vehicle take? I anticipate rust gets bad when things start to break - random things or a part rusts out that is hard to get to/ replace. Would a van with some surface rust or body rust be just fine for a few years? How fast does the rust “grow” if I leave it alone but keep the van clean and dry?

Check this CL listing out and look at the photos of the bottom get a better idea of what I’m looking at: https://austin.craigslist.org/cto/d/1989-ford-e150-4x4-van-on-33s/6573310900.html