You're probably fine. If you saw what I've been driving.....
Look at the "frame" first. Although it's a unibody, it does have a pseudo-frame that constitutes a good deal of the structure. Make sure it's not rotten, especially around the mounting points for the leaf springs. Also look at the rear, where the leaf spring shackles attach to the body. It's a complex boxed structure, and a little rust is OK, but eventually if it rots away something could come adrift. I would not worry about floor holes. You can just patch those. Likewise, rocker rust is probably no big deal until things get so bad that there's nothing left to attach to, and you start losing the bottom edge of the unibody. I've heard of some people replacing rotted rockers with a big piece of steel pipe or conduit, thus ending up with a sort of rock rail in place of the rocker. The skin part of the rocker panel doesn't seem to do much structurally, but the inner walls might, and if you're expecting actually to replace a rocker, it's really difficult if the body side of the pinch weld area at the bottom has disappeared.
The bottom of the rear quarter panel behind the rear wheel tends to rust on early ones, but for some reason not so much on later. Not critical, but check that there's not so much rust there that it's started to eat up into the interior. If the upper part of the rear quarter is rusting, you face a pretty difficult job of repair if you plan to do it right with welding, etc.
If the rear deck is rotten, it's a bit difficult to fix and keep dry, and to do it right you may need to drop the fuel tank. While you're looking back there, look and sniff around at the fuel tank itself, and check for wet spots around the seams, where rust can start leaks. Mud gets on top of the tank and can start holes, which can be patched, but seam leaks cannot. Not a deal killer, but you should bargain for the cost of a new tank if you're buying.
You should crawl under the whole thing and look and probe for floor rust. While you're at it, check that the front anchor points for the hand brake cables have not started to pull out or crack around their base. Fixable, but a nuisance. If you don't reinforce these your hand brake will never hold no matter how well it's adjusted.
If the roof is rusting out near the front edge (common here in New England) you face a nearly irreparable problem that will result eventually in a wet interior, though you needn't worry too much about structure. If the windshield flange is rusting under the sealant, your windshield will leak air and water too, but there's not much you can do to check for that until you replace the windshield.
Finally make sure the brake lines and fuel lines aren't rotten. This includes the lines that go through the inner front fender to the caliper hoses. All fixable, of course, but something you should always keep track of, and add to your bargaining list if they're too nasty.
Otherwise, if the thing feels reasonably solid, your decision will probably be mostly cosmetic, and if you like it, and it is mechanically good, it might be worth going for, especially if you're now out of the rust belt, where cosmetic repairs might stand a chance of lasting a while.
