Why not leave the weep holes open, bring the barrels up to say 250 or so for a while to make sure the void is dry, and shoot a bit of linseed into the weep hole? Tilt the barrels around to get a good coat of linseed over everything inside, and heat to dry. This is an old method for getting rid of "ghosts" that seem to be of the benign type. It should add some protection as well.
I see no problem with plain old gun oil either. I've had trouble bluing on guns with a minor pinhole in otherwise well soldered ribs. Both due to water and to oil. The oil I got rid of by injecting acetone through whatever access was easiest. I think I've had worse problems with the water. The only answer I found to work on that was making the weep hole larger, and using twisted paper towel to act as a wick, getting the water out more quickly after a boil.
Hope this helps somewhat.
Jim
