My Tiger Mast has a foam core inside it, so you don't have to be too concerned about if it is sealed. This got me thinking about my H16. I bet you could remove the mast head cap and use some of the spray foam that you buy at your local hardware store for insulating cracks. You may need to attach a small hose to the spray nozzle to get it deeper down the mast. I would still seal the mast end cap with silicone, but the foam may provide more bouyancy for the mast. We need to get Myth Busters to prove this theory.