Gerbs, there's no "recipe" in scratch-building, otherwise it would be a kit. The great thing about it is that you can experiment and sometimes come up with a new techique by accident. If the experiment is a total flop, you don't have a whole lot invested.
Whatever glue you use, test a little of on a scrap piece of foam to make sure it just doesn't dissolve it (altough some interesting effects can be had that way.)