[essman]

I have an '83 Irwin 37.
The tank started leaking 2 owners ago. He quit using it and put a tank in the nav station ice box. Not sure what kind as I never saw it.
The owner previous to me took the tank out of the ice box and made it back into an ice box, then put an aluminum tank inside the existing leaking fuel tank. Of course the cabin floor had to be taken up to accomplish this. I don't know what the original tank capacity was, but the tank put inside it holds 61 gallons.
It's not as hard a job as it might seem. Just takes some time. It's much easier if you just replace the holly/teak sole when doing it.
I don't know about your boat, but you could put a fairly good size tank under the port settee in mine. One of those rubber bladders would be fairly easy to do.....
Good luck.