Hard to tell from the pictures, so I made a crude cutaway sketch of our storage approach.

I removed a side wall, rear bulkhead, and galley.
The green is the lower storage area. Yellow is the mattress, gray are the three drawers that pull out when the hatch is open.
The purple headboard has sliding doors that access the lower compartment inside the front of the green box.
Behind the doors is under bed storage for muddy shoes, etc.
Here's a shot of the cargo deck and drawers before I built the cabin on top. Left drawer has the stove and silverware drawers built into it.

Here's the front storage that's behind the headboard sliding doors.

Now you can see the start of the cabin on top the storage deck.

Here's a shot of one rear drawer in use. they are simple plywood boxes sliding on the plywood bottom of the tear. No expensive or complicated drawer slides. It works fine. think of it as dragging a box across the floor.

The biggest reason I took this approach to the underbed storage was access and sealing. No lifting of the mattress is required, and the only seals are the doors and hatch like a regular teardrop.
Sam