If you're worried about them sliding off and damaging your toys... simply go buy a couple of large bungee cords, and wrap them around the it and the bed.
That said... I store mine in attic above my garage at home. As far as I'm concerned, the tables that come with the rig (and the poles) are worthless... both of them (main cabin & garage).
Instead, I bought a couple of folding tables from Costco, which are far more sturdy & useful. I can put them wherever I want, they're sturdy enough to use for a workbench, practically indestructible, and I store them on top of the Happi-Jac bed in the garage.