I might try the prop to trim anode test again, but on 20 ohm setting if you have one. Maybe test a prop blade to the center shaft nut, or leg housing nut, just to get an idea of where the weak link is.
I would definitely make sure the trim tabs are joined to the hull. With the hull being bare, you should not be overzinced on any metal, as long as everything is interconnected. When you connect the bare stainless trim tabs, your hull voltage will increase somewhat. You should also have a factory jumper wire connecting the leg to the low end of the swivel mount, and maybe one at the engine tilt pin. Check these.
Probably a better alternative to an ohm meter, is to have a battery powered light and run the ground circuit through your points to be tested. That way, you are driving current through the connections. A bright light means a good circuit.