Slight change of plan from the original idea. After trialling the truck camping a few times, I decided on a revised storage layout for the back. Module 3 would become a simple housing for 2 large plastic drawers that can be opened from either inside the cabin or from the rear door.
I made an MDF frame for the 2 plastic trays I already had, and reinforced the corners
Made some simple wooden pins to stop the trays sliding forward on heavy braking. The drawers are a snug fit anyway, to stop rattles, but the dowel pins hold them fast.
Carpeted the bases to again stop any rattles if the trays move. And painted the rest of the unit in grey.
Fitted in place, butted up to the module 2 storage unit.
Drawers accessible from the front or back.