The one problem with the swing-away hitch mount is that it has a long bar out to the side where the hinge has to be located - seems like that would be a big wind drag.
Thinking about it, I'd go one of two ways. One would be a completely hollow, ultra lightweight tail that clips on over the hatch. This would be the simplest to fab and hook up, but would also turn into a 5' sail when the hatch is open. However, it lets you use the car the same way as before.
The other way, which I would go prefer but would take longer, would be to remove the hatch altogether and replace it with a two-part tail. One part would mount to the upper hinge for stability, and into the trailer hitch below, and be semi-permanent. The second half would basically be a smaller version of the first option, but with the seam within the boat tail further back. Using the hitch for strength, you could extend the cargo space out about 2 feet, and not having the portion of the hatch nearest the car move, you could get a good tight seal to the car. The rear half of the hatch would have to be light and thus not cargo-equipped, but it's smaller anyways so less useful (although you could leave it open if you wanted to carry 10' long pipes).
Henry
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