After making the difficult decision to abandon the sliding door concept, visit 105 happened. It was a pretty successful day by my standards, I managed to build the new door frame AND hang the existing door.
The frame was attached to boat with fibreglass filler and will eventually be glassed in. I used the existing door to at least secure the boat for the moment. This will eventually be replaced with a door that fits, once that has happened a new hatch will be built too. After that a new piece of ply board will be fastened to the wall that has just been exposed. Workmanship pretty good by my standards.
Video of the door in operation below: