Hi Mooseman,
Calculated old school way. Filled up tank till pump shut off. Double checked with a small top off and it promptly shut off again.
Didn't want to flood my charcoal canister so considered it good
Zeroed my Trip A. Drove 243.8 miles. Went to same station, same pump. Topped off again in similar manner. 13.8 gallons
17.67 mpg if my college degree help with anything!

I was pleasantly surprised. I know I can eek a few more mpg if I slow down. I just wanted to keep it consistent with my regular driving when I do this desert trip a few times a year.
The only change is I switched to the Valvoline 5w/30 full syn. Restore and Protect and have about 1500 miles on it.