It's not just the sales folks. The only time I ever came close to running out of fuel in a boat was when I trusted the surveyor's report on tankage. Gotta trust your own eyes when life and limb is concerned. To the OP, the Pacific Cup runs every year and a friend of mine participates. The run from San Fran to the islands typically runs 3 weeks under sail. Refueling at sea, while technically possible, is so highly unlikely to be dismissed as a function of sensible trip planning. I strongly support the 1/3 in reserves trip planning model no matter what your tankage. IMO, if you can't carry sufficient fuel to arrive with 1/3 in reserves then you really don't have a vessel capable of the trip.