We don't have a Rural King either, but we do have a Shipton's Big R and a Tractor Supply which both are pretty much the same thing as Rural King. I will have to go and see if they have any of those blocks of styrofoam or if they usually get them in with some of their shipments. Thanks for the heads up as to another place to get styrofoam from.I'm not sure if you have one but my local Rural King has tons of solid while Styrofoam blocks in their lot free for the taking. They are about 12"x12"x18".I built a couple pedestals from them. When I went there they had 50+. I know white foam isn't the best but I've found burning the grout lines with a solder iron and heat sealing gave a nice finish before dry locking.