i can solve your problem for under $20.

go to Home Depot or Lowes and buy a sheet (or two) of 1/2" particle board or plywood, and 2-3 hinges. take out your current OEM board, and use it as a template to trace the shapes onto the new thicker board. cut out the 2 pieces with a jigsaw. attach the hinges, and you're done.

you might want to spray on some polyurethane to help weatherproof it, especially if you have a damp or leaky trunk.