Thanks PB; I called them said you can not connect an aux tank to another 'gas' tank by law but can diesel...whew! So they have 65 gal for $1000 $1100 if I want it powder coated black. I should done this long time ago, probably didn't want to loose storage but this box has enough and better than running out of gas. I'll ship the one I have to my son for his new F-150, cost $700 new not cheap!
http://www.4truck-accessories.com/Ford/Dodge/Chevy-GMC%282011_and_Later%29_-_65_Gal_Diesel_Combo_Auxiliary/Tool_Box_Tank/6360?offset=0&Search_Category=0&Search_Make=0&Search_Model=0&Search_Body=0&Search_Year=0
This thing has 65 gals so that put me @ 100 nice! Can't wait to see how much to fill now, $4-500 Least the gauge will say it's full longer so I don't get so depressed by how much gas I burn pulling.