Here are my DIY fuel tanks to replace the miserable old tanks from 1938 that I had to cut out of Grantala a year or two back. I've been operating from a 60 litre drum that sits between the two engines ever since.
There are six x 104 litre tanks - replacing two plated brass 450 litre tanks. The tanks are used 316L stainless steel LPG tanks from automotive use. They are sitting on a 150mm x 115mm (6" x 4 1/2") Spotted Gum bearer that is notched over the stringers.
We had a guy roll some 5mm 316 stainless strap for our fitting straps and a friend (Steve) fabricated the rest of the fittings and welded the tank fittings. The straps are probably overkill - but I don't like the thought of a loose tank - ever. Half the bolts are a mix of 16mm and 12 mm diameter, again in 316SS. The fit of the tanks is so tight that we had to stagger the straps to get it all in. Height wise, the breathers on the outer tanks will just clear the deck - and will be led to a box above the centre tanks that will also hide the fillers - and function as a step up onto the sundeck.
The tanks have a welded in drain pipe protected by a plate stand-off that rests on the bearer. I was concerned about having contact that could lead to crevice corrosion - hence the standoffs.
We had to cut off the box around the inspection plate and then made up the inspection plate covers - which are O-ringed. The centre tanks will have the fuel out and return lines in their covers - drawing from about an inch above the bottom and returning onto the tank wall. The drawings are done and the plugs turned, but not yet finished.
I haven't finished the mountings yet - I need to epoxy all the hole edges and add more bracing to the other side of the bulkhead. This bulkhead is 25mm (one inch) thick hardwood marine ply with 75 x 50 (3 x 2) stiffeners. I want to spread the mounting point load and also add significantly to the bulkhead mounting points. The side with all the nuts on it will be covered by some 1/2" marine ply that I had made up with Queensland Maple facings for my fitout.
The idea behind the six tanks is that I will normally only fill the centre two tanks - 208 litres being more than enough to take me down river and down to Sydney Harbour. If I want to go further afield then, I fill the outer tanks as needed. No more stale fuel.
I will also be adding a fuel cooler when I plumb them in. I've got a couple of Racors for primary filtration. The only downside I see to this setup is the number of valves needed so that each tank can be drained and/or isolated as required - but they aren't expensive, as they are only 1/2" fittings.
Another item nearing completion - as soon as I get the kids to polish them!