looked at mine over the weekend, it was about 80 degrees here, took it to the beach!!! The canvass just goes in the slot with very few screws in a couple of spots as you have indicated. The cabinets just screw in the top and walls. I can get you some dimensions for the screw placement, I assume there is some bracing in the roof that they attach to but I do not know for sure, do you have a 1500 LB? That way I can get you dimensions from either the front or back for screw placement.
2010 Palomino Bronco 1500LB
1997 F350 7.3 PSD