While a solid third-gen F-body is not terribly hard to come by, it has been 25 years since the first ones rolled off the assembly line, and many of them are starting to show their age in the form of rust. In the case of Snowball, an outwardly solid-looking '89 Formula, the rust was lurking under carpet, layers of undercoating, and seam sealer. If I had not planned to weld in a six-point cage, I might have never discovered the rust, and maybe ignorance would have been bliss. But once I started uncovering the rust I had no choice but to fix it before I could securely weld in the cage.
While there is plenty of good information on body repair, thirdgen F-bodies and G-bodies are not quite as easy to fix as their predecessors. First and second-gen F-bodies used a subframe attached to a unibody-the third-gen is the first true unibody F-body that must provide attachment points for the K-member and all suspension attachment points.
The third-gen's unibody is constructed of multiple layers and pieces of galvanized sheetmetal loosely stitched together with spot welds, covered in many places with gobs of seam sealers. The areas carrying the highest loads are often the most susceptible to corrosion due to the flex of the body and the nature of the overlapping bits of often poorly spot-welded sheetmetal. Road salt, combined with stress corrosion, allows rust to gain a foothold, resulting in cancerous holes.
While there is replacement sheetmetal such as doors and fenders available, I was unablem to source replacement floorpans, let alone any of the pieces that intersected the floorpans. Since the parts I needed weren't available, I knew I would have to learn how to do the job myself. Thankfully I had access to fabricators including Paul Morgan, Paul Ruggles, and John Parsons, who I bugged mercilessly for their secrets-if a magazine guy can fix his car, so can you!
Sixteen and 18-gauge sheetmetal are most commonly found on modern cars, with 18-gauge representing the bulk of it. Sourcing suitable replacement metal is essential. In the case of most automotive repairs, oiled and pickled 18- and 16-gauge sheet will cover the majority of repairs. The local home improvement store is probably not going to carry this, so some phone calls to steel suppliers will be required. You will probably have to buy a 4x8 sheet at a time. Most steel houses will not want to cut it for you, and may not even want to deal with such a small order. You might even have to drive a ways to get your hands on the stuff, but it's worth it. Oiled and pickled sheetmetal lacks hard-to-remove mill scale, and is easier to form. Don't use a stop sign, beer can, or part of an old washing machine-seriously.
Before you get started take lots of pictures and even make drawings of how the pieces are welded together so you can duplicate the factory geometry when you put it back together.
If you don't know how to weld, it's time to learn. Enroll in a community college or have a friend teach you. It's really not that hard, and once you know how it will open up entirely new ways of working on your car. You don't have to blow the budget on a high-dollar TIG-welding rig, either. An entry-level 110-volt MIGwelder from any of the big names like Miller, Lincoln, or Hobart will get the job done for around $500.