I have a 40 gallon gravity feed RDS aux tank/toolbox in the bed and I am completely satisfied. I've been using it for over a year now.
The federal rules for gas vs diesel aux tanks are different. These gravity feed DIESEL tanks are 100% legal and safe. I now carry a total of almost 80 gallons of fuel. I chose the gravity feed over a pump system because I like simple and I still think I made the right decision. I just don't see any advantage to a pump system.
I usually just flip the lever at the end of the day to refill the main tank over night if I choose not to fuel up at the end of the day. The increased range also allows me to buy fuel when and where I want to. Without the tank I would start looking for fuel after about 225-250 miles. And I am a little picky about where I buy fuel so I don't necessarily want to HAVE to stop somewhere that looks a little 'iffy'.
The RDS install kit incorporates a shut-off valve where the aux fuel line ties into the factory filler tube. When the OEM tank fills up and fuel then backs up the filler tube it contacts this valve, which closes, stopping the flow of fuel from the aux tank. This should alleviate the problem of fuel backflowing out past the fuel cap because the fuel will not rise that far.
I specifically got this aux tank because it sits one inch below the top of my bedrails allowing me to use a tonneau cover. Works well. If I was doing it over, I would get their 60 gallon tank/toolbox instead. It has the same footprint, just with a smaller toolbox.
An advantage of an aux tank is that you can transfer to a new truck if you want to.
Northern tool carries RDS, but the RDS site carries many more sizes. I have also heard that RDS will custom build a tank for you, but I have not confirmed that.
Tim
