Related comments about the fuel tanks. Fortunately, most folks don't have to ever build new fuel tanks, but if you do here are some things to consider:
West system epoxy is diesel fuel approved, according to their official ap-notes. We found a vendor selling inexpensive cored carbon-fiber panels in 4x8 foot sheets 3/4" thick. We cut it up to exactly what we wanted and glassed it together making the exterior and baffles from the same sheet material. The core keeps the panels from flexing. The tank was a fraction (apx 1/3) of the steel tank it replaced and will never ever ever rust.
In the old days, fuel tanks had a pickup that extended above the bottom surface of the tank. This tradition started before we had good filters and the theory was that the water, rust, dirt, old pop-tops, and other junk would sink to the bottom and you'd collect it in that bottom inch or two of the tank below the pickup. Some even had floating pick-ups. This is a terrible idea. By contrast, we built the bottom of the tank with about a 10° slope with all bottom surfaces leading to the fuel pick-up. That way, the random stuff gets sent to the filter quickly (especially water) where it is captured fast and the bacteria don't have a chance to grow in the tank. All baffles are set at an angle to discourage small pools of fuel and stuff collecting on the up-hill side.
We built two tanks, one on each side of the boat with a 2" pipe leading across to balance the fuel when the boat is upright (it's a sail boat). The pipe is sloped down to the centerline of the boat to discourage junk from collecting in it. At the center-line of the pipe there is a 2" "X" connector with each tank pickup leading to the port and starboard legs of the "X", the top of the "X" has a reducers to correct size to provide twice the flow that the main engine, generator engine, and diesel heater all operating at once require. The bottom of the "X" has a 10" pipe attached, a reducer to a 3/8" fitting, and a valve, and 5' long length of hose.
This arrangement allows the fuel to move freely from one side of the boat to the other for two reasons. First, on a sailboat you want to put the fuel on the windward side, so we open the cross pipe before we tack and the fuel flows to the leeward tank. We the close the valve and tack the boat providing 750 lbs of fuel to be located 7' to windward to help keep the boat flat. We do the same thing with the water. This allows us to have the rough equivalent of 18 burly sailors sitting on the windward rail who don't eat, drink, or try to hit on your spouse. It makes the old girl sail far better.
As the fuel is flowing through the 2" "X" on each tack, the heavy stuff drops into the lower leg of the "X" and is trapped. About 4 times a year I open the valve and drain about a pint of fuel into a glass jar to inspect what I've trapped. Over 10 years, there have been about 20 very small globs of water in the sample, some tiny black dust, which must be carbon dust we didn't get out of the tanks when we built them, and that's it. Hopefully, it stays that way. We last changed the filters 5 years ago. They are showing no dirt, water, or bugs at all but after 5 years of use I thought we should take a look. For the "junk" to get past the "X", it would have to make a right turn to go directly upward, avoid falling into the trap below, and get sent to the filters. It appears that this has never happened.
Key points: You do not want a flat bottom on a fuel tank unless you're willing to get in and clean the tank. A job I don't wish on anyone. You want all bottom surfaces and plumbing to lead down to a trap from which it is easy to remove the junk as soon as it arrives. You want the fuel pick up to be far above that trap. If you can build the tanks into the boat the way steel boats do, it's wonderfully efficient as most boats aren't square and have unused space around the tanks. Finally, you do NOT want the fuel fill to sit on the deck or a seat or anywhere that water can reach it. It belongs in a locker or behind a water resistant door. The fill is where almost all the water comes from, not from the vendor of the fuel. (Although most owners blame the vendor.)
