Minor issue but sea posts generate on a a small rock that doesn't touch the ocean floor (floating).
I don't know how structures are created but the datapack "ships on seas" has a lighthouse that doesn't have this problem.

I've tried "Ship on Seas" as you describe. The lighthouse base itself its too big. I don't really want to includes large structure to generate in the world.

Seaposts using the same function as Village to spawn. The structure will blend perfectly to the surrounding terrain. But I aware of this bug during development. This is an another bug I cannot fix at this time.