I think several people here have already installed under sink drawers or drawers in a cupboard in the kitchen area. I really like the idea have been intermittently working on this project.
Currently under the sink in my van there is one 3/4 depth shelf and the carpeted floor. I'm going to remove that 3/4 depth shelf and install four drawers. I'll use plywood side panels to support the drawers and threaded rod to keep those sides perpendicular to the floor and give the assembly a box like structure. The side panels will be fastened to the van floor using L brackets. I'll use leftover pieces of the threaded rod to "wedge" the structure in place by eliminating any chance of sideways movement.
I measured the height of items we carry in that space before deciding on drawer heights.
This drawer "box" will be easily removable in case I ever need to access the propane, electrical or plumbing lines that are on the side and behind it. The bottom drawer length is 18" and the three drawers above it are 22". All of the drawers are 21" wide. I'll have approx 12 sq ft of drawer space
The drawers, when closed, will butt up against the existing cupboard doors which should prevent them from opening when we are driving.
The drawer slide units were on clearance at $2 per pair so that how I ended up with metal sided drawers. Other materials used so far are two x 1/4 sheet of 1/2" plywood for the drawers and one x 1/4 sheet of 5/8" plywood for the supporting sides.
I mistakenly cut the drawer fronts too short. I can use them as is but might re-do them when I can set set up a saw outside. It has just been too cold for that type of work.