I've been pondering the options to better use the under-panel space behind the seats on my 63 Plus4, and finally did something about it. I've seen the creations of others, and this is what I came up with.
The original panel is fine with new carpet so the new storage tray simply sits below that, with the old panel sitting on top. Overall I lost 5/8" depth which is fine.
3/8" plywood with holes cut out for a pair of half-size catering trays. As the tray lips sit slightly proud, I cut a 1/4" ply panel to sit around the trays giving enough clearance for the tray lips and the sheet metal screws holding them in place. the additional slots are for the battery tender cable and seat belts.
Total time, about 2 hours, total cost under $40 for wood and trays.
Very happy. Photos via links.
dave
https://photos.app.goo.gl/Uk3u5zW8qxln6EY43https://photos.app.goo.gl/3BfCjrS1eWlkuJZc2https://photos.app.goo.gl/OXTG7ihULTl6FiTl2https://photos.app.goo.gl/XG5AD0l7ppW10UVU2