Any ideas?

You basicly just need a peice of plywood that will lay on the lip along the deck and console.

I just kept mine simple . 3/4 marine plywood for frame and decklid, put on carpet. Deck is light enough to take in and out when you want. Its held in by a couple screws that are easy to remove. Mine is still solid after ten years. If it gets wet take it out and dry it. Draw a few plans its really a simple project

I'm going to do one for myself. Just going to use some treated 2x4's to build out a frame, similar to the center area of your boat. Not going to put a back on it, just make the top a full lid that opens for easy access. Not worried about dry storage, just being able to move around without tripping over stuff. In your case, I'd frame it out and make it 2 storage compartments, 3/4" plywood carpeted for the lid. If you want it enclosed, put plywood and cover with carpet. Your configuration, there should be enough weight and the shape will keep it from shifting so you can make it removable.

You can find dry storage boxes in various sizes to put in there to keep stuff dry and you can order metal lids to install to make it look more professional. Fiberglass isn't that hard to do over the wood but is messy and I doubt worth the effort since you can seal it and then cover in carpet. Looks like a one weekend job to do.

aluminum angle iron is lighter and looks better than bulky 2x4. both will be fine though