They look good Joco.
I have been playing a bit and managed to draw out a rudder support and a rudder for my large r/c tug boat I am building. The smaller bit gets embedded and fiber glassed into the hull. The tubes in the top and bottom are good push fits, and the metal parts in the rudder itself will be pinned as well so they will stay put.
I printed these at 85% fill so they should be strong and watertight, but they will also have several coats of primer and paint.