: I will be making the form and laying carbon this weekend.

Good luck. I used a couple of strips of ash for the coaming riser on my Cirrus. Because these fit so well I ended up not need any spreaders. The seams were at the low spot closest to the shear and I just held them fast with a couple of spring clamps.

If you've built a coaming like this before you know (and if you haven't it needs to be stressed greatly) to not let the lay up rest to long on your mold. Make sure you provide an effective method/material for a mold release. I lingered on the Cirrus coaming and let it stay on the mold for two days. It came off very hard and I stressed/bruised the glass in a couple spots getting it off. The household plastic wrap I used wasn't a great choice either and I was a couple of days picking bits of it out of the underside of the layup. I ended up cleaning the underside of the coaming with a pneaumatic driven fiber wheel. It came out nice.

Dave