SSB - where can my ground plane be?

I'm currently planning my SSB installation and I am using special copper paint for my ground plane (just like using copper plates). However I cannot find 3 square metres of floor under the sea level. I have a number of options but perhaps the best is the lazarette. However only about 1 square metre is beneath the sea level and actually touching the sea. The rest is either above the sea level or on a wall not touching the sea. Does this matter? Will I only get 1 square metre's worth of grounding, even if all 3 sqaure metres is painted?

Any help appreciated.

[James S]

My ground plane isn’t connected to the water and I don’t think it is supposed to.
Its also not below the water line.
Mine was made by installing copper tape to the top of the wooden frame work that supports the two aft bunks on the same level.
All the tape joints are overlapped and solder.
I haven’t heard of the paint product you propose.