I made a template on cardboard, then picked up some sheet mettle from Lowes and put it together. I put the back seat back in and besides the package tray, you would never know it was there. The sheet mettle I used added a little weight, but it was cheap (and I was in a hurry when I built it)....I would go aluminum if you can find it.
Note: Be sure to check the regulations before building it. I think there is a specific thickness of mettle required, but I don't recall what it is...and it is different depending on the material used.
