A simple spring bolt latch will do it.
Ive used them in the past for compartment door latches, inverted so just the handle is exposed.
Stupid simple and clean enough.
Paint is whatever the painter is using. I didnt get specifics, but it is an industrial 2-part epoxy primer + 2-part industrial top coat. The shop routinely does heavy equipment, and is well known for doing very good work.
That paint job will simply seal up the steel. The visible frame, and all aluminum skins, once finished up will be top coated with U-Pol Raptor Liner.
Once done it should be a lifetime bed. At least thats what Im telling myself