Some alu sheet metal work. The larger box took me a bit to get the hang of welding such thin aluminum, and distortion was a pain due to the pre-bent flanges (scrap), but I got there in the end. It started life as a bit of channel bent scrap. I notched the flange in 4 places and bent it in my brake... then welded some salvaged plate onto the sides. Needed to have a steel backing to keep from melting holes, and had to clamp it over every weld to keep the distortion from opening up the joints.