I wanted to have a semi permanent box in the trunk to keep the extra filters, water, tools from rolling around in a jumble. I decided to throw something together simple with some leftover fiberglass. I maybe a form out of cardboard and tape. Then I cut some small coolant hose to slide over the top edge to make it more rigid. Fiber glassing it 'in place' was a little messy, but I did remove the carpet and fabric first so no harm no foul as far as I'm concerned.
Then I cut up some brackets from the scrap bin and fastened them in place and ran a second layer of glass and resin.
after it was cured I pulled it out and removed all the cardboard and tape and trimmed of the excess glass. then I added a bit more hose and layered up a bunch of glass and resin. The next day I trimmed it and ran the flap disk over it.
Then I sprayed a few layers of a few different colors of whatever paint was almost empty on my shelf.
Light, Sturdy, Removable, but most importantly Inexpensive....