You are in the rust belt so they rust in places you cant see, under the plastic cladding and rocker panels.
Look at the front of rear wheel wells inside, use a screwdriver and poke around a little, that's where the rust will be.
If there is rust there pass, it will be a big job. Check the rar brake backing plates for the E brake, these are commonly rotted away and require removing the rear axles to change.
Frame rust isn't a big issue but the air ride is, they commonly fail and are an expensive item, the compressor is right behind the drivers side rear wheel and poorly protected from the elements check it for corrosion and make sure it works.
The fuel pump is another weak spot on these and is a bit difficult to change due to the size of the tank, there is no access hole. It either works or it doesn't but if its loud expect to change it sooner than later.
The engine and trans are pretty solid units, the cooling and electrical systems are usually trouble free unless someone keeps dropping change in the front lighter socket (this is very common) that blows the fuse that also feeds the OBD II port, short it a few too times and the thin wires to the lighter will burn through and short.
