I don't know.. I guess it depends on the ratio of wood to fiberglass? Make the 'glass thick enough and it'll probably do just fine! But don't ask me what "thick enough" looks like; I've no idea..
Have you looked through the Inca Plastics catalog
? You can tell they're in the business of making tanks, not web sites and sales materials, but if you can get past that they have quite a variety of options. I bought several tanks from them for my bus. It worked out particularly well because I "needed" to make a trip to the southern California area and they weren't too far out of the way to stop by their factory and pick up the tanks, saving the shipping cost.