Smart design, man! That should hold up well without requiring any kind of permanent attachment. Only other thing I would do would be to cut a curving slot in it where it will overlap the middle of the trailer. Then put a bolt up through the top of the trailer at that spot with a big flat washer and nut on it. When you hook up the trailer, run the bolt through the slot in the aero panel and put the washer on top to loosely secure it. That way it will stay relatively tight to the top of the trailer and not flap around, but the trailer can still turn freely beneath it.
How hard was it to set up that cruise control? Does it set by speed only? It would be awesome if it could be set by mpg. What kind of mpg range are you seeing using it? I could see there being a wild swing of mpg within a couple of miles an hour on the Insight, how sensitive is it?
I always use the cruise control on my wife's Explorer to speed up or slow down, rather than using the gas pedal. I'd say I have it on 90% of the time. By keeping the cruise on as much as possible and clicking it one or two miles an hour at a time to speed up or down, it holds the rpms (and mpg meter) way more steady than I possibly can with my foot on the gas pedal.
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