hey good deal I didn't know where to point you to find a cork big enough but it looks good. I know that airplanes use cork on their floats and they are sealed with some kind of resin or glue an aircraft mechanic might be able to help. Or contact EAA and ask them what was used to coat cork fuel tank floats in the past they should have an answer. I used to belong to EAA 20 years quit cause I didn't like paying dues seemed to be getting too commercial and my airplane took enough beating sitting on EAA'S flight line during the airshow at Oshkosh all the security was at the war bird area and none in the experimental area. And what does EAA stand for Experimental aircraft association not war bird association. getting off my soap box.
ride it like you stole it.