Here are the Trimlock pictures I promised. The first shows a piece of Trimlock.
The next shows the Trimlock on my new truck between the topper and the cab. The open end of the "C" part of the Trimlock is mounted on the edge of the 4 mm Okoume marine plywood I used for the skin of this topper, which I built.
Incidentally, my Scangauge was not properly calibrated and was reading about 10 % high. So I really averaged about 29 mpg on my last tank of gas, and about 34 mpg on the highway.