Large cheap pellet trap for teaching

I shoot mostly indoors with my son, who despite thinking he is Sam Fisher, is still working on becoming a good shot. I have a small metal trap I use but he was missing it and hitting either the door or the plywood in front of the door and sending pellets all over the target area. I needed to make something big enough to catch the strays so I took an old rubbermaid bin a little bigger than a laundry basket, tossed in an old sheet of plywood on the bottom. On top of that I tossed in a couple of old couch pillows and then using 3 cans of Great Stuff foam (get the super expanding kind) I filled the bucket and waited till it dried and then we just tape targets to it. Many hundreds of shots later, it stll works brilliantly with no bounce backs or outs and no need for repair. Give it a try if you need a cheap indoor trap.