Glad I stumbled on this again. I never did get the photos, I sold the truck and recycled the cover.
The cover has a ~2' section in the front that is secured with bungee cords underneath. This was hinged to a bolt down 4' section. The entire thing was sized to fit the outer width and length of the truck bed and sat on top of the rails.
The rear section had 4 holes drilled into it just inboard of the sides of the bed.
Through these I dropped large bolts (1/2 inch by 5 inch).
I welded angle iron to nuts to fit these bolts. nut -> [||]_| <- angle
This allowed me to hook the lip of the bed by touch and not have to reach underneath to do the bolt-down.
I still have the bolts and nuts, I will attempt to photo them in the next couple of days.
PS: I live in the "Pacific NorthWet" and never treated the plywood. More than 2 years in the weather, it's just dark, not even sagging.