I debated material to use for the tray support panel - plexiglass, Lexan, etc. I ultimately decided to use this smooth-finished 1/4-in. thick “crafts plywood” panel obtained from local crafts supply store for about $6 - simply for ease of cutting it and attaching items to it. After cutting out tray template, I spray-painted it black to match trunk interior.
This panel was thus very easy to work with, and provides adequate non-flexing rigidity and support.
A dimensional sizing template for the lift-up support tray panel is shown on the next page.