There are different generations of fiberglass used on the Corvettes throughout the years. The 1953 Corvette, being the first, had the most unusual fiberglass. This was hand laid fiberglass using fiberglass cloth. Fiberglass cloth has the uniform weave, looking much like a screen door. If it is used today you will have what is called telegraphing. This basically means the checker appearance will be visible is the final paint. This is the reason why it is necessary to use fiberglass mat. It is not uniform, but is disorganized, with the strands running at random. This type of glass will not telegraph through the paint.
For the previous statement to be true there must be enough primer covering the fiberglass. It is best to gel coat the finished fiberglass repairs. Usually this would include the entire body. The body parts, doors, hood, deck lid, and trunk lid would be optional as deemed necessary. 1953 - 1957 Corvettes are the most likely candidates for gel coating. 1953 and 1954 we can call first generation fiberglass.
Sometime around the middle of 1954 gel coating ceased. The hood, deck lid, trunk lid and sometimes the doors would be in the 2nd generation fiberglass. These parts were press molded (smooth both sides). In 1955, the entire Corvette was done in press mold type fiberglass. We will call this the 2nd generation fiberglass.
1958 Corvettes through the 1962 Corvettes would be the third generation fiberglass. This is a better type of fiberglass. The methods were better. Around the hood opening there would be even hundreds of cracks in the 1957 Corvette, likewise all the openings for the doors, trunk, etc. The 1958 Corvettes through the 1962 Corvettes didn't have this problem. This makes the repairs easier and less costly. Other higher qualities would show up as you work on the 1958 to the 1962 Corvette. The 1963 to 1967 Corvettes are even better yet. Other than repairing a wreck, there are usually only a few cracks at the corner openings of the windows, hood, headlights, etc.
I do a resurfacing to the 1953 - 1957 Corvettes. I call this method, "reskin", which is to cover the body with a layer of fiberglass. After all the repairs have been completed, I use a 3" rubber pad with a 24 grit sanding disc and an electric drill. I slowly rough the area to be reskinned. 1953 and 1954 Corvettes usually need the entire body done. 1955-1957 Corvettes, maybe just the body only, not the body parts.
Reskinning a Corvette is a long slow process. Grind the entire body with 24 grit to really scuff the surface. Use fiberglass mat, not cloth. Apply one layer of 1 1/2 oz fiberglass. This type of fiberglass is the general thickness you will buy from most stores. Use a roller designed to roll fiberglass. This will roll out the bubbles and bring the resin to the surface. The strength is in the fiberglass. The resin is the bonding material. The resin does not have the strength. It is necessary to have total saturation of the fiberglass. You will know you have total saturation when the fiberglass turns totally clear. The type of resin to use is laminating resin. Do not use casting resin. Casting resin has wax in it. Resin too thick will be hard to saturate the fiberglass. Resin too thin will run off onto the floor. If the resin drains out of the fiberglass, the glass must be removed and the process done again. Allow the reskinned areas to cure at least 24 hours.
Now that the fiberglass work has had time to cure, you must grind the glaze off top of it. Grinding the glaze insures adhesion. Now spread a thin layer of bondo over the areas of work. Sand the areas until a good contour is accomplished. Never use bondo too thick--1/8" at the very most in a bad area, or else you must use fiberglass to repair it. Use 80 grit sand paper or coarser when sanding the bondo. Eckler makes the best bondo for the job. The final step is to gel coat the Corvette. 1953 to 1957 usually needs the entire body gel coated. 1958 to 1962 Corvettes may be gel coated where necessary. Again, Eckler makes the best gel coat for the job. During the restoration of the Corvette body, the more sun the better. As much curing in the sun as possible is best. Let's say your Corvette has been painted, assembled and ready for show, if it never leaves the garage this is okay. On your first three-day car show in the hot sun, you will see if your efforts survive.
The main key to making sure your paint job survives is to always work clean. Clean hands and clean rags all the time. I cannot stress this enough. I never have bubbles appear in my paint jobs because of my constant efforts to remain clean.