My 2 cents is that if you are new to 5th wheels then you might slow down on what you "think" you must have. You are going to get lots of opinions from others, what they do may not be right for you. As another mentioned there's the weight of the fuel to consider, it costs you fuel mileage the more weight you carry. Just like other issues like membership campgrounds, you may want to travel for awhile before you invest in an auxiliary tank. We've been fulltime for 12 years and never had auxiliary tank, gas stations are everywhere, even on the 2 lane highways. Sometimes we carry 5 gallons of extra diesel, most times we don't fill it. In the 12 years we've needed it once.