I have a little upholstery business on the side and just threw away a bunch of foam. What you need for gluing foam is contact cement. I use it in commercial containers, but you can use 3M 77 in the spray can from Walmart. Lightly spray both sides, then stick it together. It'll hold with no problems. You could also use Styrofoam, it may be better than foam rubber?? The glue will work on either. With the styrofoam, it can be shaped pretty easy and may give more support. Good luck! If you want me to save you some foam, I can, but I bet you could get all you want from a local upholstery shop.