Almost finished my build, need help finishing up

Mounting double boxes on the flatbed, "looks" more finished, personally and slightly more usable/convenient (like ad-hoc work bench when open). They'll also stay in nice shape longer.
The challenge of the tie-down points is real though. Not sure what to do there unless you can make something like Bedlam's setup work. I'd be shooting for something very similar to what he did.