I wonder if NASA would build a pressurized replica of the actual HAB to be used on Mars at Johnson Space Center and put it completely underwater like the "Deepcore" underwater oil platform in the film The Abyss
a half-completed nuclear reactor facility in Gaffney, South Carolina, ...a depth of 40 feet
NASA already trains underwater at
Aquarius Underwater Laboratory, part of NASA's Extreme Environment Mission Operations (NEEMO) program
Located 18 meters (6 feet) under the surface
or a period of 12 days.
The lab itself is a coral-encrusted cylinder that looks a lot like a yellow submarine, located 5.5 kilometers (3.4 miles) off Florida's Key Largo and it's the only underwater laboratory in the world, as close as NASA could get to replicating space conditions.
Astronauts Train for Space Missions in Underwater Laboratory
18th of May 2007,
as well as spacewalk work at Neutral Buoyancy Lab (NBL) at J.S.Center.