I've been on the beach at low speeds (<35mph) and back roads at higher speeds (~65mph) and the Revolver X2 held up well. I can't say the same about the BakBox, but I never had a problem with the cover opening, collapsing or coming undone. The terrain at the beach was pretty bumpy, but the gravel roads I was on were fairly smooth. Still, I drifted a few times and fishtailed here and there, but the cover stayed on.
The BakBox collapsed and fell off the rails, but I've since fixed that problem by using an L-bracket on the clamp that secures the strap. The L-bracket holds the BakBox back against the top plates and doesn't let it slide forward. Haven't had a problem since.