Hey John,
My Bad. I just read the initial post and he was asking about cowl flotation. I agree with Bert , but I include it as a structural part of the cowl. Here's a pic of one of my 8255 hulls with flotation built in - Styrofoam, a couple layers of light cloth with West epoxy, and I sprayed Clear PPG when I clear coated the hull/cowl. Also gives me more strength where I handle the cowl.
Old technology?? Pshaw !!! Har, Har !!! This has always been my preferred way of building. In addition to being super strong, the only part of the hull that is accessible to water is the tub. A couple well placed drain holes allow that to drain as the hull runs, keeping the hull CG and weight the same throughout the run. The hulls are my own design, and if changes are needed, a die grinder and a sanding block with 30 grit make short work of it.
Remove the cowl and hardware and they make one hellova Boogy Board. CHEERS !!! Bob