Custom Gas Tank

[CMBarnes]

I am looking to add another gas tank in the forward compartment of my '75 23' cc ( the fish box in the floor in front of the console). If you look on the specification page of this site you can see the area I am talking about. Does anyone know how many gallons this area will hold? I have yet to measure it myself. Also, can anyone recommend a good custom marine tank fabricator. I know a new tank might be pricey but I need to add more fuel because of my twin 200 setup on my bracket. Any help would be appreciated. My deck is finally out but I have been busy at work and it has been slow going.
Thanks, CMB