I don't have the Enkay flaps, but made my own to function like them, only better.
I would get several sets of the rubber parts, and cut them as needed for the different vehicles. Go to a truck supply place, and you can buy the heavy duty flap material rather inexpensive.
Yes, I think that 3 to 4" of clearance when loaded is a good height, assuming the flaps are mounted at the very rear of the TV as the Enkays are.
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