I drew out my cockpit plan on a computer and then printed this out and traced it onto the deck. Then using a grinding bit, I removed the "cap" from the deck exposing the foam underneath. Then it was back to the world of styrofoam dust as I ground down the seat area with a wire brush drill bit. Experimentation with a variety of tools found that a narrow trowel was the best for making forward progress in the leg areas. Then I used a linoleum knife to hack out cross hatch patterns and then scraped away with my hand towards the side walls. As I got closer to the inside shape I wanted a large gravy spoon ended up being the best tool, much like scraping out a giant pumpkin, though it actually reminded me more of tunneling a snow fort.
Once I was able to scoop out enough to sit in, I was able to continue to expand it so that I could position my knees up along the inside of the cockpit rim in the style of Riot kayak's outfitting style which I've grown to love in my river kayaks.
I then did a couple coats of micro on the inside, but things were still very rough.