Yes. Unfortunately these were just put in place with some sealant, and not properly tabbed in as they should have been. Of course if they are tabbed in with fiberglass, it the tank or hose has to be removed, then the tabbing would be cut.
I would grind any mat off the back, and build a new core, with any material--from foam, plywood or balsa--doesn't really make any difference here. Plywood is available, and I would seal it with epoxy and put a layer of cloth on the back, seal the edges and the access port with epoxy. It will last the lifetime of the boat then.
The next question is how to put it back in place. I probably would use some very narrow tabbing, with 6oz glass and epoxy, and paint the step with something like KiwiGrip. One of the bed liners would also be an option. You could use "Hatteras White" paint with some micro beads mixed in. Lots of options at this point.