We always carried 3-4 Gerry cans of diesel for long distance passages. Never can tell when something is going to screw up and contaminate or drain a fuel tank and you'll need some clean fuel. On cruiser/racers and/or small boats tankage is minimal. Currently have 20 gallon tank which will normally do me fine on a voyage. Unfortunately, an equipment failure on the last passage meant having to power over 200 miles back to do repairs. That pretty much drained the tank and added fuel from the Gerry cans so as not to run dry. If I had larger tank(s) would end up with a lot of unused fuel over long periods. Current tank was filled several years ago and still has plenty of fuel in it. Wouldn't want a larger capacity tank because of that. Way better to carry Gerry cans for longer voyages than have stale fuel, that is if it does get stale.