Why so many through holes? why don't you do a single larger through hull with a manifold? I like solid through hulls as few as possible and easy to reach as possible.
Did you mention how many, what for, how far from the cleanout? Maybe running all that hose exposes you to more problems than it solves. Except for the aforementioned defective seacocks, they are really nothing to worry about. Nor are they hard to install or move if you should have to.