Interesting thread. I have never used anything but my Rhino spray in bedliner with my previous Lance and now my Palomino. No sag anywhere and it's never slipped at all even in off camber off road ventures. But then...newer trucks have thinner metal beds,
My 97 F350 tailgate weighs around 50 pounds. My buddy's 2013 Silverado tailgate weighs around 20 pounds.
I was surprised. We loaded my quad in his Silverado using my aluminum ramps on the tailgate and when he drove the quad in, it tweaked the tailgate. Never had that issue with my older Ford.
Lighter is better, but not where it counts.