This has been a very interesting and informative thread. As the OP I thought I should summarise what I now intend to do after reading all the helpful contributions. I now have a Clamshell vent fitted in the stern of my boat - from here the wiring from the solar panel can easily pass through to the inside of the boat in the rear berth area. I am buying a 40W AKT Solar Panel Kit (which includes a regulator) and I propose to mount the panel to the boat using an NOA adjustable pole mount fitted to the aft port-side stanchion.
All I need then are some sunny days - not guaranteed here in Sweden!
The following link probably won't help you out, but someone here in the states it might. SolarBlvd where I've been buying my panels has a 40 watt on sale now for $89.00.
We have two 5 watt solar plates, swivel mounted on the port and stbd stern pulpits, respectively. The wire pair from each plate goes thru a separable connector sheltered under the plate and then down thru a drilled hole in the topsides above the rub strip and into the aft bunk area. A blob of silicone sealant seals the wire entry hole. Renew the silicone blob every 5 or 10 years as needed. Not pretty, but it is effective , cheap and not very noticeable ( less so now that the boat is 10 years old).
Ron
The panel is a 26 Watt Solarmare panel. The wiring is taken into the boat through the clamshell vent shown and led under the rear berth to a regulator mounted on the aft wall of the heads as shown here:-
That came out real nice and looks to be very adjustable so you should be able to get the most out of that panel. Thanks for the follow-up and have you posted pictures of the build and possibly a material's list. I think there are a lot of people out there that this size or one a little larger (40-60 watts) would really fit there needs. We need more, but most people don't,