External fuel tank mounted in bed - thoughts??

I have a 100 gal in bed and 39 under. I hauled TTs and Boats and use a farm pump to fill the main. I can go from VA to OKC and buy 2.29 diesel and run back. It paid for itself in 1 trip. 100 gal diesel weighs 8lb/G. My 3/4 T can gross 22,000 and I weigh 19500 with TT loaded and fueled. I get 10.8-10.9mpg at 67 MPH. Anyone who says they get better than that can hook on my trailer and we'll see about that. No one has ever come and hooked on it to prove their 20 MPG Dodge Cummins, Ford or Chevy.