I constructed a bulkhead gasket, to prevent blowback, made from Gorilla weatherproof duct tape. Heavy rain storms have been passing in our area and so far there has been no leaks from the polycarbonate panel cover.
Just a thought ... For those DIYers that don't have an aluminum welder setup or can't find a local welder then try this - use plumbing PVC instead of aluminum for the support ladder frame or grid. Plumbing PVC is very cheap and easy to obtain, cut and glue. Now they have a one step PVC glue instead of the old two step with PVC softener and glue. The nice part about PVC is that it is very light weight and I believe by using it could reduce the cost of this project by a least $150. You would still need some metal for the hinge and gas lifter/strut sections. You could DIY easy prototype/simulate the design, still using the corrugated plastic roof, without gluing or securing the PVC pieces together.
If Corona virus-19 strikes next year then you might see another PVC "all plastic" truck bed design project by this Ohio hillbilly.
BTW - My Ranger gas MPG is slightly increasing using this corrugated truck bed cover and best of all
my gas cost is only ~ $1.59 per gallon with no place to go.
The question that everyone is asking me is "where can I get Aluminum?" for this truck bed cover project.
I use two vendors - this is not an endorsement - there are many other suppliers.
1. Metal Supermarkets (locally in US cities and online)
2. Metals Depot (online)