The first outside corner I tried just 'smooshing' together... but this doesn't work nearly as well as the welding tip and laying in a bead of material from a rod. I bought a used Liester on ebay, and it tuened out to be pretty effective. The speedweld tip was easy to use on inside 90 degree joints and didn't take long to get a reasonable feel for. The box doesn't have to be super strong as the panels are all bolted to the rails.