I'm interested in mounting some kind of safari rack to the topper on my truck for my spare tire and more lighting. Is this wise? Would the fiberglass support the weight?

Awhile back when I had a 91 & 94 standard cab trucks both had shells we used to jump up there all the time. I remember once having three people on top if it , and it never felt like it was going to cave in . I also had a yakima rack built in but never really loaded it up too heavy.
Anyhow my vote is that it is indeed safe if your topper is of the type that is made from thick fiberglass.
hope this helps,
Richard