Almost finished with the one side. I strongly suspect I *won't* be using this technique again as it is simply too time consuming. I also don't know if I will be able to get the edges relatively straight. Hopefully it will be taken care of in the edging, but I won't know if it will work until it is started.
Showing this photo again because it's what I have of the styrofoam. The shapes are cut out and I've started shrinking them. Turns out that, unlike the clear number 6 plastic, styrofoam doesn't shrink evenly. It has a grain line that it shrinks along. Sometimes this works with where the holes are punched and sometimes it just makes for an awkward lumpy mass. With everything being cut out before having the hole punched I have no way of determining what that grain line is so I will probably need to do some experiments, unless I decide that it isn't worth the trouble at all.