I like to do "Pull Tests" to see what holds the canvas to the foam the best. The test is simple. Prep your foam, then glue a 6 inch by 12 inch strip of canvas to it in whatever way you want to try (Leave about two inches off the edge to grab the canvas by.), wait for the glue to dry, then pull off the canvas. The one that pulls off the most Pink Foam is the winner. I'd rather have the foam be the weakest link in this scenario than then glue.
I've done several "Pull Tests" with TBII at different strengths. Using a 50/50 mix, I found that almost no foam is pulled off with the canvas when I test it. That does Not mean that it didn't stick the canvas to the foam. As a mater of fact, the canvas held to the foam very well and it took some strength on my part to separate the two. As many people here will testify, it will last forever this way. Because the canvas is held on in such a big area (As in the entire side of a camper) this is plenty of adhesion for our purposes. The wind, even at highway speeds, doesn't pull on the canvas as hard as I do during my tests.
The problem is that the people of this forum were used to Glidden Gripper. This was a wonder product that was readily available and had proven itself. Everyone here is looking for a replacement for that. However, it really isn't necessary to have that much adhesion power for our purposes.
I still suggest gluing the canvas to the foam with full strength TBII. Then after it dries, fill the weave with 75/25 or 50/50 TBII. This will help preserve the canvas. Then be sure to paint it with a Quality latex primer, then paint it.