For my Endeavour, I built up 5 layers (to 5/8" thickness) and it has worked out very well. My lip extended 1/2" originally, then sanded back to just less than 7/16". If you are building the coaming according to Ted's methods, I would recommend one more modification: avoid joining both layers of the lip lamination at the centreline (fore and aft) - instead, build the top layer with solid pieces that span over these joints (will require some pre-bending with steam, but its worth the trouble). This will give you a much nicer curved-top coaming, rather than one with a ridge. Good luck.