Round them over before you cut the miters
I thought of that too but not sure what the joined corners would look like without trying on some scrap 1st. Seems like the right idea....Round them over before you cut the miters
My sketch gives the wrong impression that the corners are mitered. Instead, the corner joints are box joints so there are some subtle issues here. Until you have built a splayed side "box" with box joints, you may not fully understand the issues. I was hoping there was a box builder in the "crowd" that had faced this issue. The attached picture shows a prototype. The narrow edges of the stock were not beveled first. After the sides are beveled, both top and bottom, both bottom and top edges of assembled box will lie on a horizontal plane. In the photo, the corners do not meet nicely.Round them over before you cut the miters