I have made a cargo cover from a piece of vinyl sheet and two pieces of dowel, plus two curtain rod holders. It did mean drilling 4 holes in the trim just behind the middle row seats, but I can live with that.
My third row seats are removed and storage drawers are fitted. It would be tricky otherwise.
Click the link in my signature to see some photos that show the cover. On my website click on CARPUTER HARDWARE.