Reply to "Making Masonry Walls and Bridges – Fun with Foam"

You can get the pink foam at HD or the green/blue foam at Lowes.  If they don't have a size smaller than 4' X 8', you may need to cut it to fit in your car.  Since it makes a mess, they probably won't cut it for you.  Some sheets come pre-scored, but if not, it is easily scored with a carpenter's square and box cutter razor knife.

Yes.  You can make the portal with one piece of foam.

DON'T use white Styrofoam.  That will ONLY make a mess in my experience.