This is not a towing issue but hope you will help. My crew cab Lincoln LT has a 5 1/2 foot bed. I plan on making a 4 hr trip I will have 2 sheets of 8 ft plywood will need to leave the tail gate down....
I bought a used cover and had to get it home on the truck, now i had the tail gate up, but this will also apply to you. I just used a ratchet tiedown to hold the cover on. I also have a crossbed box in the bed and it pushed the cover out back by another ft or so. No issues in almost 200 miles.
So if you have concerns lock it down with the original hardware and use a tiedown to make up for peace of mind. How do you plan to secure the plywood?