I raid the offcut pile for nearly all mods. Probably don’t want to use plywood but any solid wood is fine if it’s encapsulated in epoxy. Mine are one and another spices of mahogany and sapeli. I’d never go out and buy it special, it’s left over from furniture projects. Pine would be fine, poplar from the big box store would be too, oak and maple don’t hold epoxy very well. And you’re right, it was a stock build, mods completed much later.   

Hey, thanks for replying! It is super helpful to have heard directly from the person that came up with the idea. I will have a look around at my offcuts. I have a limited amount of ash on hand and some others that you mentioned are not great with epoxy. I may have other stuff but it is likely too thin for this application. Are you still happy with your placement?

   Hello from newbie guys, looking forward to learn a lot from you guys

   Kind of a fluke Dustin, don't check in here very often any more.

If I were doing it from scratch I might put the lower tie downs directly in the bottom panel fillet before it cures. Save a couple of steps that way. Thwart height on the mid level sections seems about right. They work great in conjunction when securing duffle bags. Might get away with one strip down the middle in aft bottom section. Would keep floor of section between 2nd and 3rd thwart clear. This is where your feet will be most of the time. The upper sections, the "supperd inwale" sections, come in very handy for fenders and all kinds of things. Again, left the seating section empty because I don't want to lean against a thin strip of wood. If I were doing the inwales at build time I'd take care to get them well integrated to bulkheads and breasthook.

What ever way you go, if you pre-make, epoxy and varnish the strips like this...

before installation you'll save drips and sanding headaches. If it's your first build the planning headaches might not be worth it though.

   Thanks a lot for the recommendations. Most of my sailing will be in the Chesapeake and a smaller lake in PA. Eventually it will go with me to Oceanside, CA. I want to be able to easily attach additional flotation and your solution I the best that I have seen.