Designer 35RLTS and Jayco Talk...Thanks Frank!!

I would guess that it's maybe 1/2" or 5/8", but it should be easy enough for you to check. Remove the little screw to slide the access panel on the rear of your storage area. Look around where the elec panel is. There's a hole cut for a bunch of the wires to go through. You can check the thickness there. It's definately OSB though so I would think about through bolting your slide or getting another piece of scrap wood on the bottom to spread the load.