Nice truck!! Does it shut off when you stop?
I would try this one...
https://www.autoanything.com/tonneau...edCovers_Shop2
One of the better ones allot of trunk owners are using. Did you look into GMC hard tri fold before you bought the truck. How long is your bed? I don't know if locking the tail gate is enough of a lock, if you want a locking cover then you may have to go hard plastic?
Mine is GMC factory tri fold and keeps everything super dry. Do you have a spray on bed liner?
https://photos.app.goo.gl/XkpfG7pPHpiUW7Fg7
https://photos.app.goo.gl/t95HofwjYaTf5KZF8
Dave
67 Nova Boy