Inside corners? You mean the "tab" bends? That's just careful eyeing with a vice. Actually I use a couple of scrap metal bars to keep the vice teeth from marring the Al.
I trace and rough-cut out the shape on a flat piece of metal, trim with the nibbler, dremel sand all the corners, file the edges, and then bend with a vice and hammer (hence the marks on the bottom). If I think of it, I'll drill countersunk holes in the end tabs for the screws (holds the vecro in place) before bending the tabs. If not, I use a flex-shaft thingy to do the countersink. It takes roughly 3-4 hours per tray and it's all by hand. If there is an easier way to do it using the tools I have on hand, I'd LOVE to hear it! lol.
As far as making something, it's really too time-consuming for me to charge a fair amount (for both you
and me). I have the
ones in the pic for sale, but they are an oddball size. If they'll work, let me know and we can iron out the details.