Sheet Metal Locked Corner Seam

I haven't worked in sheet metal before, so this is probably easy, but I'm getting stuck.  I want to create a rounded box from sheet metal with locked corner seams between the corners of the box and the flat parts.  I'd also like to create holes to bolt and secure them together.  Basically, I want 4 flat pieces with hemmed edges and 4 corner pieces with hemmed edges to fit together with bolts.  Here is a diagram of the joint that I'm trying to make by hemming the edges, I'd just like the 90-degree radius to be 1 inch: 

Is there something easy that I'm missing?  Here is the link to my public document: https://cad.onshape.com/documents/3f3baa9d239d7f1875d04440/w/5f8a951408371f2f948597e1/e/e480237dc93575b8a72aff2e

Thank you in advance for any help!