Well Randy you really do not have a 40, but a buggie. How much fuel do you carry on Meanie? I know I started with a full fuel main tank with only 30 highway mile on it and carried 15 in the Aux tank. I used all but the Aux tank traveling along. Most with 80's used there mains and had some poured in at one time or the other. So most burned close to 22 gallons or more on the bigger vehicles.
I do not record the acutal miles of the trip, but the book states about 140 miles for the whole Kokopelli trip.
What was not included in the actual trip are the side we took, like Top of the World, the Delores river water crossing, and the trip on the highway and back to Onion Creek.
So I would guess I average with my truck about 8 MPG for the average of it all. I would guess when I did the scout trip, moving at a different pace, I got a better MPG, may be burned about 15 gallons.
But one needs to move at the pace the whole group can, so more fuel consumption is going to happen.
I do not know if that tells you what you want Randy, but a few of the bigger rigs may of made it on one tank if we did not go back and forth to the onion creek trail head to the Dewey bridge(about 40 miles highway on lower tire pressures). Plus going back up to the trail split the next day to back track up to the split at the top of the trail (about 5 miles all up hill on dirt and traveling slow).
Hope that helps Randy, what do you figure you get offroad in you Buggie? How big is your fuel tank in your rig?