The double floors in the alloy hulls are not sealed chambers. Water
can and does slosh from the bow back to the drain point in the transom. The inner floor is both for strengthening and to provide a flat area on which to stand.
I think that they are great! My 3.5 meter Hypalon Gemini
dink has an advertised empty weight of 47 kilos. The hull
is now about ten years old, constant usage by cruisers who anchor
out continuously, and despite a bunch of scratches through the powdercoated finish, plus being burned by the druggies who stole her, there is no corrosion
nor other problems visible.