Its A Good Upgrade
Per, I have the OD25, but our respective placement of the holding tank can be similar.A previous owner installed a 20 gall plastic tank under the V berth, snug up to the front (wide) end and vented to outside. It is rectangular and rests on a plywood platform. There is a square piece of mahogony plywood facing the salon to cover the tank, and a removable wooden window piece has been installed to keep an eye on tank levels. Clean-out deck fitting was run straight up to the side-deck, and a vent was run to the hull side, high up.I don't use the tank, as a porta-potty serves my needs, but the tank and the marine head (stored away for now) are available if I need to. Not many other placements are available on our respective boats, especially so close to the head.Don