You may have seen this idea out there in General Automotive. I believe it is something in which many members are going to be highly interested.
The basic idea is that with a full tank (how else?) a group of chapter members start around a course that is laid out with "waypoints" where chapter volunteers are standing by with "Waypoint Cards" to prove that each participant made it to a "checkpoint".
At the end, tanks are refilled with a chapter judge recording the gallons put back in the tank. Filling up anywhere along the way is grounds for immediate disqualification..
Courses can be long or short, and should include historically or otherwise significant way points, and factor in enough time for stopping and taking pictures.
A loose "RALLY" that is not only a challenge, it is an opportunity for families to drive around sight seeing, it brings people together as a team, it would promote mileage improvement, and ought to be one heck of a lot of fun!
The course would be flexible in this way: You have to touch base at the waypoints. They are the only places you can get a card. HOW YOU GET THERE is up to the individual - so the route is up to each team to decide on.
Who do you think would be interested in such a game?
The beauty of it is that since it is about mileage, not speed - all of it can be done without special dispensation, closed roads, or breaking the speed limit anywhere on the routes...
It is "WITHIN THE LAW".
If there were a commercial scale (such as at a truck stop) at the beginning of the course, total weight could be factored into the fuel consumed for the final point score, so it would be fair across the board.
It's a concept I am still working out the details of, but the precedent is the "MOBIL Economy Challenge" which you can search out on the net.