[s_forbes]

A word of caution: Some of those frame parts are only attached with one rivet on each bracket. I suspect that those will be able to rotate and the rivets will shake loose quickly.

Are you planning any kind of cross bracing for the frame? As a fun experiment, grab two opposite corners of the frame and push them together, then pull them apart. If you see a lot of movement, that's a sign that you'll likely need more support in those directions.