The paint has dried, so I have glued in the various parts of the book shelf unit, squeezed the cats cradle of wires into the allotted space and turned it all on. Amazingly it all works. The only bit that doesn't is the battery meter, where I know a wire is loose, but it was never of much use anyway. It always showed a full charge until the battery was flat, so I never based any decisions on it. The USB port works fine and is so much easier to plug a cable into than the cigarette lighter socket. That will just be used to charge the handheld VHF. So now I can run everything at once, which might possibly not be such a good idea.
The GPS and compass will store in the space under the switch panel, so they are close to hand.