So I bought a roll Hoop kit from @Low Rider and so far all is going well. I've had an issue changing the locks on the storage box once before in the past and I eventually figured out how to do it but I've forgotten again, rather than taking every screw out I thought I'd ask here 
The lock I'm referring to is the one in the middle
The lock I'm referring to is the one in the middle

- I put the new inner box into the old outer box (including existing locks). The only fiddly bit was lining up the thin metal re-enforcing strip which fits at the rear between the two sections.