I have a rectangular frame that I want to keep from flattening into a parallelogram. The frame is 8' x 4' and the members are 4 7/8" high by 2 5/8" thick.
There isn't a particular load that will be pressing it into the shape per se, but I want to prevent this from happening through incidental forces, because this rectangular frame will have some load on its flat side.
I want to avoid having to make corner to corner crossbars because the size of the rectangle makes it difficult to do this and I am also using wood joinery without screws or brackets. I have considered adding supports across each corner.
Is there a better/cleaner way that does not involve any 45° miter of any kind? I feel like there must be something obvious I am missing.