Why does the anode get all the attention?? Galvanic corrosion requires several things to occur. An anode, a cathode, an electrolyte and a conductive path.

In addition to maintaining a coating on the anodic mast, it would also be beneficial to paint the cathodic SS hound. More beneficial, in fact, because another variable in how quickly the anode corrodes is the surface area ratio between the cathode and the anode. A scratch in the protective coating on the mast near a large uncoated cathode will produce more concentrated corrosion than if the mast were unprotected.

The conductive path. If the hound was bedded with a dielectric sealant and the rivets installed coated with the same, it would minimize (in addition to what you've achieved with the paint) the conduction portion of the circuit. The RTV would also minimize the electrolyte getting into the joint. I don't know the dielectric properties of the RTV sealants readily available at auto and hardware stores.

The electrolyte. In this situation with the mast-hound joint, it's a very small circuit. Since the mast is out of the water the majority of the time, the circuit will be that small crack in the joint were dew or rain can collect and work with the salt that has collected there. A dielectric RTV filet could prevent that from happening. I think that this mechanism would also negate the usefulness of a zinc sacrificial anode because the sacrificial anode has to be part of the circuit. In this case, attaching a zinc to the mast won't prevent the galvanic corrosion since it doesn't share the same electrolyte path for the ions that the mast-hound circuit does. However, the zinc anode would protect the mast while the boat is turtled.