Need a bigger fuel tank
 

I have a 1986 Jayco motor home on an E-350 chassis (7.3 liter turbo diesel). The coach has two tanks--the forward tank is about 18 gallons and the rear tank is about 22 gallons. I'd like to have a larger rear tank for vegetable oil fuel. I've heard that a bronco tank, at 33 gallons, is an option. Does anyone know about this or have any suggestions?
Thanks!
Paul