how thick would you need to make a fiberglass encloseure to equal the strength of 1/2"-3/4" fiberboard?

Any clue of how many layers of mat/application of resin this would take?

dont know how thick to equal that but right now i have 2 orion hcca's and i used 5 layers of mat and a whole lot of resin i made till it was about 1/2" thick and its been holding out nicely even with those big ass subs

I don't know how thick it really needs to be, but my enclosure is at least 1/2" thick and it has help up well. I don't think fiberglass will really save you much weight - it just makes it easier to do custom installs.

most installers i know use mdf as a base and then put the fiberglass and over that(there is also body filler or bondo used when you want to make a smooth rounded area then the matting is placed on top of that then the resin is applied