I had an RDS 30 gallon aux tank installed on my F250 earlier this year. I love the flexibility the extra fuel gives me in planning my fuel stops. One thing I discovered about my truck however is the fact that it seems to have a vent on the top of the internal tank. I discovered that the hard way when I left the manual valve open. What a mess. I installed a solenoid valve in the fill line and wired it to one of the upfitter switches in the cab. Now when the gauge gets down around 3/4 of a tank I'll turn the valve solenoid on and watch the level slowly rise while I'm driving without risk of overflowing the internal tank. If I forget to turn it off when I cut the engine no worry of overflow since the circuit is only hot when the ignition is in the on position.
For me the aux tank was the cheaper option even though I had the aux tank installed professionally.
