I'm applying this to my roof this week. I can already tell it makes a big difference in interior temps. Much cooler inside and you can rest your hand on the roof in direct sun. I used their Aqua-Primer, Bus-Kote and Flexi-Clear. It is all water clean up and non-toxic. http://hytechsales.com/
(snip) But the finished product is great! (snip)
I also have the fiberglass caps front and rear. Consider this a top coat to your existing roof (metal and fiberglass). So, if you have loose paint, cracks in the caulk or other potential leakage you have to fix that first before you put this on top of everything. The paint job is only as good as the prep you give it. Given you have taken care of those issues, then you can put this on the fiberglass and metal roof. I used their primer with their ceramic insulation additive that I mixed in myself, if you use some other primer, I'd ask Hy Tech about compatibility. I hope that helps.