Additional fuel tank

[Tsuru]

Our Mk2 Catalina 36 has 3 potable water tanks. #1 = 35 gal under the V berth, #2 = 21 gal mid tank behind the engine and #3= 21 gal startboard aft. We also have a 16 gph watermaker.
Each of these tanks has a dedicated deck fill and vent. The aft starbord tank is fussy and likes to leak when full. I put a large O ring round the clean-out and it’s better, but that said I keep the tank empty.

This same boat has a 25 gal diesel fuel tank and more fuel capacity would be nice.
I looked into having an aluminum fuel tank fabricated to replace the aft Starboard water tank. Instead of making it a full service fuel tank the current thinking is to utilize our spare lift pump and batch fuel into the main tank when needed.

The tank resides in a molded in compartment with a wood lid screwed in place.

Does this solution sound workable? Any obvious ABYC or other standards design flaws?

I’d appreciate input and ideas.

Thanks,
Ray