I appreciate the compliments and am glad that you are enjoying it. I've done a few and this is by far my favorite and most versatile build.
I ran the tank as dry as I dared, filled it up with 40.1 gallons. I got 582 mile out of that liquid gold, equating to 14.52MPG. I figure I could have squeezed out another 10-20 miles but I couldn't risk it. The tank seems to gravity fill since it is mounted up higher than the main. Once about two thirds of the aux is gone they both start draining at about the same rate. Once the main goes to three quarters the aux is empty. During heavy weather changes it will throw evap codes but they go away when the weather stabilizes. It is similar to what I experienced when I had the Man-A-Fre setup in the FJ. Overall very happy with it. I'm sure that others are getting better mileage than I am and could get more range out of the extra 18 gallons but it effectively doubles my range. I highly recommend the mod to anyone interested, and CBI did a great job.