[dscott]

dakota, The only time I've seen any spider cracks are when something is stressing the fiberglass or something has hit it. If you are sure they are spider cracks you can sand and fill them. The way I've seen gelcoat repaired is to use a die grinder and follow each crack to the end, refill with gelcoat, sand and polish. If the crack goes deeper than the gelcoat a new layer of fiberglass would be needed to add the strength back. I would check to make sure nothing is stressing the firewall. The other thing I have seen is air pockets between the gelcoat and fiberglass. This will generally flake off when exposed to heat or stress. This may be the problem. The areas usually look like bumps or pockets on top of the gelcoat. With those you could remove the bad area, regelcoat or use a filler, sand and paint to match. Luckily the area you are talking about is pretty well hidden from view so it won't be as critical visually. Hope this helps.
Don