A number of members have interests in that area, one has a little applicable experience…
@ellmer built one ferrocement submarine at Lake Attersee, in Austria. The hatch seals were damaged by someone that broke in, so it took on water and eventually sank.
He began a 2nd one, in Cartagena, Columbia, which has gone unfinished. IMHO, the construction of the unfinished one was probably discontinued due to the drug-sub phenomenon and the international war of drugs, but Wil Ellmer has not been forthcoming on such information.
My own interests don’t exclude underwater housing, but don’t lean that way directly. My ideas for a circular area for IMTA, within an enlarged version of the Japanese Puffer Fish ‘mandala’ nest to regulate waves, could potentially provide a zone of relatively calm waters, that would potentially allow for undersea habitats, in the relatively shallow waters on the Continental Shelf, in the Gulf of Mexico.
It is my hope to create a base of operations to build and launch ‘Gulfsteads’/Seasteads, have a land-based support point for food, parcels, mail, etc.
While I do not have the funds for a down payment and closing costs, I do have a likely space selected, with several acres, along a highway, with a potential build area and roadway that could become a launching ramp.
There are some semi-sheltered waters, but it would need dredging, to create a viable channel.