This modification adds shelves above the rear deck, aft of the rear seat-back, essentially doubling the amount of storage space in this area. I decided to add the shelves because my rolled up bed-roll would drop into the lower storage area when stowed, making it more difficult to recover when setting up the bed.
I originally placed the shelves on top of the framing, but found that doing so prevented the seat-back from lying fully flat when reclined. I redid the mod with cleats along the 2"x4" framing to allow the 1/2" shelves to fit flush in the framing. I use 1/2" x 2' x 4' premium grade plywood from Hone Depot for these mods because of the tight grain and smooth finish.