Well, all I can tell you is that they are a huge PITA to install and get sealed properly. When I ordered mine from the ARE dealer, I knew from the look on his face that he wasn't all that thrilled with the order! When it came in, they had to make a special brace out of 2x4s on the inside and use tie down winch straps to suck it down tight enough to get the bolts in place. It also needed one guy on top for weight! After a couple of hours, they got it on.
First time washing the car, it leaked like a sieve. Took it back in, they removed it and then tried again. There is also some gooey gasket gunk that comes with it from the factory that has to be used as well to assure water tight fit. The gaskets are really tricky to seat right and twist easily, especially given the tricky install! I was advised to not remove it, unless I didn't care about it being water-tight, which I don't plan on anyway. Also, given it fits so tight against the cab, I was told to expect paint damage from friction rubbing....
Definitely not the same as installing a cap on a pickup, since you have the whole issue of fitting it to the cab itself and not just a free-floating fit like on a truck.
All in all, I am happy with the ARE cap and will not be removing it. I suspect it might be easier to install without the gasket seal and the gunk, but then you have the water leaks to deal with.