I am looking at a getting a Arkel Utility basket (its actually a bag) that I plan to lay on its back on my rear rack. It has a hard bottom that will make lifting the bag and the 25 lbs of battery and controllers and chargers not wear on the bottom of the bag.

The bag is 19" long and the rack is 13.5" long. The rack itself slips in between the rear seatback causing a loss of about 2" for wider items.

I think I could easily find a piece of sheet metal that folds out from the rack or slides out over the exiting rack while the proposed bag is being used.
This would simply be there to prevent the bag from drooping down.

I would rather have a longer rack, but I am open to suggestions.