I too owned an old Hatteras (1981 56MY) which had integral fuel and holding tanks down the middle, the water tanks consisted of a semi-molded in unit and one along the transom, again all centered and molded fiberglass. Great design in my opinion, helped keep CG low and made use of space otherwise wasted on a lot of boats, a freed up a lot of space otherwise occupied on many boats. I've been pretty active with other Hatteras owners, and have never heard of anyone having an issue.There are a lot of 35+ year old Hatts out there still doing fine. I'll qualify that as it seems to me someone must have had issues with the gasoline powered boats which Hatt made a few of, and Ethanol; I just haven't run across one.
I've been told by old Hatteras hands (a lot of them around here, and a few of them did work on my boat when I owned it) that it is a more expensive design to do correctly.