get a 1x4x6 #2 pine board for $2.46 and a brass plated aluminum (non-magnetic) door kickplate 6x36 for $10. Send the 26" you don't use to the next builder. The kickplate will have holes pre-drilled in it, too. Size the pine to screw the 6" kickplate directly to it or rout a narrow rabbet to accept it then put some "stop" molding where the screws go. You can cut the kickplate with any power saw but sandwich it between sacrificial pieces of plywood to keep metal shards from eyeballs.

After you miter the 4 pieces lay them out edge to edge. Use masking tape to connect them pulling and stretching the tape. 2 pieces on each connection to even the strain. Carefully turn them over to expose the angles and apply PVA or urethane glue to each surface. If you use polyurethane don't forget to dampen the wood, first. Also, it's very runny so apply tape the length of the joint on the outside to keep the glue off the surface.

Now set them on edge, form them into the final box configuration and tape the remaining joint. Place the chassis on some waxed paper to save Wifey's cherry dining room table. It will peel off easily after the glue dries.