Auxiliary fuel tank

I have the same truck. When we first went full time and started traveling I really felt the need to keep more fuel on board. I never really had the desire to make my capacity 70 to 80 gallons, but I investigated maybe adding another 25.

What it came down to for me was actual need. After the first several months (maybe 5,000 miles) of traveling I discovered that a 200 miles range, or about 3 hours was enough and I really didn't mind stopping for fuel. Actually we have found that we rarely, if ever, have to fuel more than once per day while pulling FW.

I have four 5-gallon diesel cans, but generally only carry three of them. They fit nicely in my bed tool box and are easy to pull out and refuel with. Depending on what part of the country we are traveling in, sometimes I have diesel in them and sometimes I don't. The point is, if I need to I can actually leave in the morning towing with as much as 46 gallons for a range of over 400 miles. Total cost of my "auxiliary" fuel supply was about $40.00 and that included aftermarket easy-pour spouts.

I know many RVers like the idea of hauling 70 - 100 gallons of fuel down the road. I have considered all the arguments of doing this, like being able to shop around for better diesel prices. But if I am hauling 500 - 700 pounds of extra weight down the road I am going to get less mpg, even though I may have just saved .10 a gallon filling up with that 100 gallons. Yes I have saved $10.00, but if I get 10mpg that day instead of 11mpg because of all that extra fuel weight, then I have used an extra 3 or 4 gallons to drive the same 400 miles. I spent about $15.00 to save $10.00.

In my mind if I spent several hundred dollars on an auxiliary tank I had better really need it plus I would want it to pay for itself in a couple of years.

Gravity fill is ok, if you have an automatically closing valve in the system. A solenoid valve that will close when it looses power. Open gravity flow is illegal in many states.