instead of those two metal bars, I would still use wood. you can do a simple corner piece and still have it in line, and not off to the side.
if they get bumped when full, it could collapse, but otherwise, great idea!
(I build these, but to keep 300+ Pound outboards on... thus the reference to use wood since it will not bend like that thin metal for the brace, think of it like a soda can when full, as long as it's straight, you can stand on it, tap the side and it collapses instantly...)