Yep, look out for rust. Mechanical bits and running gear are much easier to replace.
The worst areas are the lower front panels behind the bumper, wheel arches, rear corners, bottoms of the doors, basically the bottom 6 inches. Inner and outer sills, chassis rails, out riggers, jacking points and cargo floor all rot underneath. Check around the windows as well.
Is it a "known" vehicle, any previous history?