Last year I installed an RDS gravity fed 33 gallon tank. Since I limit my travels to no more than 350 miles in a single day that gives me more than enough range to wait till I can drop off the trailer at the RV park before searching for fuel.
I discovered that my truck internal tank has a vent on top which WILL leak fuel if I don't turn off the manual valve. I installed a solenoid valve powered off one of the upfitter switches. Now when I park the truck and remove the key, the valve shuts off. This modification saves me the embarrassment of leaving a puddle of diesel fuel on some parking lot.