What holds the rail?

So I put a cheap tonneau cover (Oedro Trifold) as a stop gap until I get what I really want.

When I tighten the clamps to pull the cover down towards the bed cap, I notice the rails get pulled up.

I wonder if this rail is sturdy enough, what holds it behind the plastic bed it's screwed on to? I got the feeling it will warp especially combined with our 3 digit Arizona heat ?

What's everyone's experience?

Thank you

 

it's not the strongest rail, but it sounds to me, that you have the clamps for the bed cover way too tight.
I had a soft folder and now have an actual fiberglass topper, and neither setups have pulled the rail up,, or out of place. Gravity is holding them down, you are just snugging them to keep them from shifting over bumps or hard braking.

 

^^This. I bought my ARE topper in June and the clamps for it attach to the rail. Haven't had a moment's problem with them.

 

With these polymer bedsides and floors, bed stiffeners are nearly a must. Especially if one is running a bed cap.

 

Yup, I added these about a month after I bought the topper: