Use more glue in order to get even coverage put 1/4 water in the glue and it will spread a little evenly put the glue on the canvas and the foam. sometimes The canvas and/or material must be almost wet. Don't get discouraged in the end your use of gripper and the liberal art of putting it on will act as the "second" glue. I showed some of the glue put on and spread on one of the shelves I did the same to the canvas. I never once did anything to the foam to make it stick. Don't get so upset that the canvas has areas that it didn't hold. Use the glue it is ok you will use a lot. the canvas will stick if you coat it. You will have to use some water in the glue to get the viscosity so it will spread evenly.
Gripper is a latex, I thought something was wrong with it when I first opened the can, it is very thick When I was rolling the paint I kept reminding myself that it doesn't have to be perfect thin coat. I just gave it a fast coat then I let it dry, get very dry. then i looked and thought I really messed up. it was rough really rough, then I sanded boy was I surprised it doesn't take a heavy sanding, light will work. A second coat will get the spots filled and even the surface out, use a brush in those hard to coat places. After sanding you can top coat with a simi-gloss exterior latex paint as the final coat.
If there are some problems I used vinyl spackling in a place there was a hole in the canvas. by the time I painted it with the gripper and sanded it you cannot tell where the hole was.
Mary C.