I know several members here made their own transom board. Here's my version of it. Made it from 3/4" starboard in seafoam color. The channel is 1/8" thick annodized alluminum fastened to the bulkhead by 4 aluminum rivets and 1 countersunk SS screw per side--the SS screw was used because there is a wood mounting plate in the way. The bottom of the board has a EPDM self-stick gasket that worked surprisingly well. I filled in the gaps near the bottom of the channel with a big dollop of silicone, smeared some Vaseline on the board so the silicone won't stick to it, then let the whole thing set up creating a perfect seal. So the transom board should be adequately water tight.
I'm pretty happy with the way it turned out. I liked the splashwell but it took up some valuable real estate. It also make access to the bilge ridiculously difficult. The bilge pump switch for the 2nd bilge pump that I had installed about 12 years ago failed so I had to remove the splashwell. (The cause was a corroded power connection where the 3 wires (pump switch, cabin switch, and bilge pump) are spliced together. The factory installed spliced also showed the green powder signs of corrosion but they used a bigger butt connector so it had more metal so it was still working but would eventually fail. So check this connection when you have access to it.) One of the best thing I like about the new setup is that I can lift the board up and hose the cockpit down like you would a pickup truck bed. With the splashwell and the 2 drains not at the corners of the cockpit, I had to walk side to side multiple times to get fish guts to work down the drain. When I was commercial striper fishing, I had scales by the handfull clogging the drains--not good when you are drifting thru 6' rips at Monomoy...
I'm pretty happy with the way it turned out. I liked the splashwell but it took up some valuable real estate. It also make access to the bilge ridiculously difficult. The bilge pump switch for the 2nd bilge pump that I had installed about 12 years ago failed so I had to remove the splashwell. (The cause was a corroded power connection where the 3 wires (pump switch, cabin switch, and bilge pump) are spliced together. The factory installed spliced also showed the green powder signs of corrosion but they used a bigger butt connector so it had more metal so it was still working but would eventually fail. So check this connection when you have access to it.) One of the best thing I like about the new setup is that I can lift the board up and hose the cockpit down like you would a pickup truck bed. With the splashwell and the 2 drains not at the corners of the cockpit, I had to walk side to side multiple times to get fish guts to work down the drain. When I was commercial striper fishing, I had scales by the handfull clogging the drains--not good when you are drifting thru 6' rips at Monomoy...