I just read through the thread again and wanted to feedback what I heard. Please correct me if I've missed something.
There are four aluminum stringers bonded in the underfloor ballast areas on all v-drives. These stringers bond hull to liner, and prevented the SX boats from just dropping in custom nylon tanks. Instead, the spaces were sealed during construction and now the entire underfloor space in those areas on the SX is wet, including the four stringers.
In the S22, the same four stringers are present, but the spaces were not sealed. The port side is pretty close to being sealed, and the main leakage is probably between hull and liner which could conceivably be sealed if enough access holes were opened up to reach the whole hull/liner joint line.
The S22 starboard side has these same issues, plus the space is not closed on the forward end. To seal the stbd side, you'd have to cut enough access holes to seal the hull/liner joint line AND you'd have to structurally close the forward end.
I'm unclear as to how the SX tanks were sealed and why the hull surface inside the tank would be any different type of fiberglass finish than any other piece of the bare hull (not sure where bare hull can even be seen besides in the depth finder hole). The mention of the foam leads me to believe that the SX tanks became tanks because they closed out the forward end of the stbd space, and then paid more attention to how they laid down that syntactic resin before dropping the liner into the hull.
I know that all the boats used that syntactic resin to bond liner to hull, and hull top to hull bottom. It's the blue stuff, and it's heavy. There's no way they would've filled the entire underfloor space with that stuff. If for some reason they filled the space, it would've been with some typical foam like that nasty creme colored stuff.
In the S22, you could run bags in there, but because of the two stringers within each compartment, you'd have to do a very complicated bag to get a lot or most of the space. Or you could punch several holes and lay a fillet of sealant between liner and hull and close off the stbd fwd end and make wet tanks. It would sure be nice to have some images from inside there.
In the SX, now you're talking about doing the patented Calabria floodgate system using your in floor tanks. I love it, good luck!!! As soon as someone cuts one of them transom holes, we could really get some great pics inside the tanks. I bet an S22 guy could seal the whole joint up to the battery area through that aft hole.