Pstatic fluid = ρgh where
ρ = m/V = fluid density
g = acceleration of gravity
h = depth of fluid
1/2 acceleration of gravity should allow for double the depth of fluid (IE 300 meters deep on Earth should be the same pressure as 600 meters on a planet with 1/2 the gravity of Earth).
The problem with these underwater structures are the one time events, like an underwater earthquake/tsunami event. A disaster is often a 100% write-off scenario. Maintenance becomes key, as long as the structure is well maintained, 200 years existence is reasonable.
The most remarkable thing about this expression is what it does not include. The fluid pressure at a given depth does not depend upon the total mass or total volume of the liquid. The above pressure expression is easy to see for the straight, unobstructed column, but not obvious for the cases of different geometry which are shown.
https://en.wikipedia.org/wiki/Hydrostatics#Hydrostatic_pressure for more on Hydrostatic pressure