Has anyone made a custom hard tray above their rear PNP bags for storage? I've seen the bungee style hangers but I want something more stout. I place a fairly heavy 3 person tube back there and am concerned the bungee style system won't be nearly strong enough. I would like a solid floor above the PNP sacks. I'm having some custom made 300lb. sacks so I'll have about half of my storage space still available. Pics if you've done it would be great!