Ross,

You might like to consider strip building the floats just like a stripper kayak, but with a heavier laminate than the common 6 oz glass. This would take care of two things: no plug to deal with after the floats are finished, and minimize the problems associated with cored construction. Foam cored composites have had a significant problem with core/skin delamination in powerboats subject to high-speed "slapping" loads. One fix for that problem is to introduce a stronger core (such as cedar strips) or eliminate the core and use stringers to stiffen the panel. If you go with the foam core floats, consider building the plug just like a stripper. I found that fairing a cedar-strip kayak was easier than fairing a glass boat plug built using the common approach of rough strips and lots of fairing compound.

Sam