Stephen seems right on his point that the ideal condition of the carrier would be to redirect currents upward so that they over-shoot the lower, flatter portion of the Pod. You "could" try for that angle, but it might look weird to try to place the carrier in a forced tail-up position on your camper shell.

I'm thinking that because you picked (or have) the shorter, wider carrier style, that's the best shape to break up and reduce the strength of air currents enough so that you gain a benefit in lower wind resistance, especially when towing through a headwind. You could test m.p.g. on a 200 mile stretch, then add the carrier for a similar 200 mile stretch, and compare results, if you have a bit of a "physics" side to you.

Whether it makes a difference or not so much, you'll still get that great extra storage cavity for say, medium weight, less moisture-sensitive camping objects that would otherwise take up room beneath the truck topper. It's probably worth putting this carrier to work, as long as the cost of the needed brackets, cross bars and other pieces isn't discouraging.

When I used to have a Thule rack on my Century topper, Thule made flat metal mounting plates (with gaskets) called artificial rain gutters, which remain attached to the topper, and to those, you attach the rack's foot assembly.

My topper was gloss white, so I just pre-painted the rain gutter plates gloss white too, so when the rack was removed, the brackets were somewhat invisible. Systems may be different now, and some toppers come with an installed pair of parallel aluminum mounting rails up top.