I dumped 5 gallons of catalyzed resin into the keel yesterday. Catalyzed it with 1% catalyst to maximize working time (at 60 degrees F it is about 4-5 hours). I also thinned it with 10% acetone. It was like a very thin corn syrup, but not exactly water. I wanted to see how well it would seep to the bottom. Well, it didn't make it to the bottom at all. Probably not because it cured, but more likely it STUCK to the ballast on the way down (though thin is was still sticky) to leave no resin to hit the bottom.
So, gravity and thinned resin won't be enough. I will have to look into some vacuum approach and draw the resin in from holes in the side of the keel.