You have to think like you're building a boat..a big ass boat, that will be able to keep steady-ish in the waves you expect.
So you need to have something like 60% of the weight BELOW the waterline. Does that make sense?
If the waves are making it rock, you need a lot more weight underneath the water so that the change in buoyancy as a wave passes by/through doesn't cause it to bob. The bigger the wave the more the buoyancy change that will happen, so you need to do a bit of imaginengineering.
Smoke a bowl!