Well… I asked a few more questions, most notably from a refrigeration expert at Miller and Miller in Seattle. It turns out that the fiberglass in the FRP sheets is actually laid out in all directions not just one and because of the optimal resin/glass ratio and the high pressure it is in fact very sturdy material. He commented that throwing a gallon can of pineapple juice against it with all your might would not damage it at all. As such he suggested that ¼” was much too thick and in fact he had used as little as 1/16” to construct iceboxes.
The only downside he mentioned about the material was that it is quite heavy.