All that is required is a stiffening brace or spar mounted to the inside of the lid. Something with tension adjustment (length) would allow for application and then adjustment to pull the ends into alignment and would allow for adjustment going forward based on weather, etc.
When I first got the truck the doors locked very quickly when I started to drive. Lately, I've noticed it may take me driving over 20 MPH or sometimes 1/4 mile or more before the doors lock. It's not consistent, but not at all like it was a month ago. Anyone else?