Sean, I've been following you "massive" project with much interest. Concerning the voids in the original ballast lay-up, they were probably responsible for the steel shot rusting to the extent that it did. If that shot were completely encapsulated in resin it probably wouldn't have rusted. I would not recommend polyester resin for your lead shot implant. I've built a number of boats (currently working on a "Beach Pea"), but I've only used polyester resin once. The odor was so strong that I was convince my lungs were instantly rotting. I will never use it again, not even if it were free. Even after it cured it continued to outgas. It got so that I couldn't work on that boat or even get near it. After the boat was painted the smell did disappear. However, I have noticed a strong polyester smell in the foreword most locker on my M15, twenty-one years after manufacture. That stuff is downright nasty. Maybe a less expensive epoxy would work well for your application. I get epoxy for Joe Merton; http://www.mertons.com/index.html He has System Three for about $375 for (6) gallons. There are epoxies much cheaper yet, like Raka: http://www.raka.com/EpoxyPricing.html They have (6) gallons for $265. There are others also which are even cheaper and being that you're using it as a filler only would be adequate. Rick Langer M15 #337 "Bluebird"