Most that are doing fiberglass walls are doing "vacuum bonded". A plastic bag as such is laid out on a big bench, a length of Filon (fiberglass) is laid on top, then the foam insulation with wood or aluminum framing around window, door, awning wire runs and other mounting areas, (Not all manufactures do framing), then the inner wall paneling is laid on top, (or bottom if reversed). A moisture activated adhesive is added between layers. Then the bag is sealed over the whole assembly and a vacuum is pulled and everything is cured as a complete assembly. This makes a very strong and structural wall. Windows, doors, and other holes are routed out. Aluminum siding is usually stapled to wood framing with fiberglass batting insulation in the walls. I like Filon walls as being better built, although heavier, however aluminum is easier to repair if damaged. You can Google Filon, vacuum bonded and stick framing for info.