I put the foam in there all at once and it expanded more than I expected so I had to trim a lot of it away. I think this led to all the pinhole leaks and frustration. So if you're going to try it I would recommend that you lay it down in several layers to build it up slowly.
Cool, thank you for the info! I was going to create a terrace going down into the water portion, so the layering method is definitely the best approach. What type of foam did you use? I'm planning on using Great Stuff expanding foam.