Hi, Barb. You are right on track. Fiberglass tubs are essentially made the same way that fiberglass boats are. And repairing fiberglass crazing and pressure cracks is a lot easier with some experience. So, if you are close to boating centers that would be the place to start. Auto repair places would be a second choice because other than a few special vehicles, like the Corvette, there are not a lot of cars made with the same kind of fiberglass as your tub.
But I wonder why you are installing a tub that already has problems.