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The Metan job is beautiful but I would bet it cost $15,000. Since you have the floor as open as it is already why not "make" a blade for a sawzall out of something like a discarded batten from a sail or some other material that will cut through the foam but not the skin of the floor or bottom. Sort of create an electric carving knife. Serations could be made in the blade as needed and you could make it pliable enough to follow the contours. I have removed a lot of similar foam [used as a spray insulation on the roof of buildings] and if you can detach it from the substrate it could be removed in fairly large chunks. You would still probably have to use the long wire brush idea to get back at the transom.