Results on my "crazed" (checked) fiberglass repair
I know some skeptics will say "wait another year or two" and let us know, and I will do that too... but I can't fastforward time, I can only give you results to date.
When I bought my 2001 Class A it had the dreaded "alligatoring", aka "crazing" aka "checking" on the fiberglass panels. The story goes that there was a defect in the panels during these years that allowed the crazing to happen over time. Mine was unpainted, it was just white gelcoat panels with graphics over them. The crazing only happened under the graphics (which were dark colored) and at the edges of them. This made it clear that the defect (at least in mine) was exposed because of heat. Those dark colors would be too hot to touch in the Arizona sun, especially in the summer. I never measured the temp, but I would not be surprised if it was around 180F or higher. My graphics were toast also.
I was told you cannot repair it short of new panels. I decided to see if that was true because I wasn't prepared to spend that much money on redoing the whole rig.
What I did was remove all the graphics and sanded the exterior a bit. This removed all the high edges of the crazing. To fill it I took an epoxy based body filler (cream) and applied it all over the crazed areas to fill it, and then sanded again. I later found a spot I missed and used a regular urethane filler and it appears to have held up as well. From here I primed it with an epoxy primer and then painted it with a high quality (but not expensive) base/clear using a 2 tone scheme. I used SPI for the primer, Wanda for the base coats and SPI clear coat.
I don't recommend painting yourself unless you have a decent gun with very high volume air supply AND have an indoor place to do it. Mine was made difficult because I had a large, but still sub optimal air compressor and had to do it outdoors. Otherwise it would have been cake to make it look it great and not a drawn out project. If I had to do it again I would have taken it to Mexico. I spent close to $2k on materials IIRC.
Since I knew the heat is what was causing the crazing I kept it white for the primary color and made the two tone a light beige. Even in the peak of summer I can hold my hand on the paint of either. The beige gets warm to the touch but not hot.
It has sat exposed now in the Phoenix sun for about 2 years. This is the second summer. Not one single crack or craze has developed.
I just wanted to give hope to those who have the same issue with their rig and don't have the money to invest in repaneling it. Even if you did it doesn't often make sense to spend $20k doing cosmetic repair on a rig that might only be worth $20 to $30k.
The key is you need to use light colors. Anywhere you have a dark color I would bet the farm it will be back within a year or so of sitting in the sun, and even a medium dark color (medium grey, blue, etc) I would expect it to return. If you are trying to test your limits on how dark you can go I would paint a metal panel and sit it in the sun for an hour or two. If it is more than just warm to the touch I would avoid it. The dark color schemes can look amazing, but it is tough on these panels that suffer from the crazing. It also makes your rig a lot tougher to keep it cool inside when you're in a warm part of the country, so there are practical benefits for opting for a light colored scheme even if you really liked the darker scheme you had.
I will report back on how well it fares down the road, but I really don't expect it to have any issues. If it would I think the entire panels would have shown the crazing after 15 years and not just the parts under and adjacent to the extreme temps. Without extreme heat to cause areas to expand there is reason the cracks should emerge again since that is really the only form of stress on them.