People do dilute gripper for the making of Poor Man's Fiberglass. After adhering the canvas to the foam, people take Gripper or TBII and dilute it to a 50/50 mix and coat the canvas. The idea is to get the solids in the primer, or glue, embedded into the strands of the canvas. This is supposed to prevent the canvas from rotting over time. They put a coat of 50/50 on the canvas, it takes several days to dry completely, (some people use several coats and I've even seen some people sand the canvas between coats to get the canvas to soak up more of the 50/50 mixture), then they use full strength primer over that, then good exterior paint.
Remember, we are not experts and we are still trying to find the very best, and cheapest, way to make a homemade camper. We have yet to come to a consensus for a standard way to make PMF. The closest I've come up with is the 9 steps I use to adhere the canvas to the foam. After that, talk to GPW. He's the one with the most experience with PMF.
To tell the truth, for me, the experiments are half of the fun.