Here is what I'm thinking. Some of you know that I rescued M-15 from 24 years of neglect in the woods. The interior plywood was shot. Under the center plywood, or what was left of it, I found many various sized pieces of Styrofoam. And more under the cockpit too. I got to thinking. Could I use expanding foam in place of the Syrofoam, and gain another storage compartment? 1600# of water divided by 8# per gallon = 200 gallons of water (x) 231 cubic inches per gallon = 46,200 cubic inches. 46,200 cubic inches divided by 1728 cubic inches in a square foot, means I would need 26.73 Cubic feet of faom to offset 1600#. Are my numbers right? Would the expanding foam damage anything inside? I know it is extremely messy, I'd control that. I'm asking if anyone else has done this and if so, was it good results? After looking at it, that I could open up some space in the cabin and in the back. Another question. I notice on the Montgomery website, that owners have used several different options for dealing with the transom mount. If I decide to change out the fixed glassed mount for a retractable one, are the nuts embedded under the transom so I could just take out the bolts, install my new bracket and tighten it back up? Or does someone VERY skinny have to get under the cabin and remove and reattach the nuts? Kendall Docter Bossier City, LA M-15 #164