With my Boat Safety inspection due next week I was thinking through the safety requirements and recalled that you are not allowed to lay electrical cables in contact with polystyrene insulation. This is because when PVC (commonly used as cable insulation) comes into contact with polystyrene, a chemical reaction causes the PVC to degrade and can melt away. Something to do with plasticisers in the PVC.
Well the route from the hole in the roof where the cables enter, to the side trunking, is all against polystyrene if the cables go above the ceiling lining. Now it gets technical, because I looked up the spec of the solar cables and they are not PVC but EVA, a more rubbery material. So is this still a problem? Well so far I don't know. If anybody out there does know then I'd be glad to find out.
What I might do is wrap the cables in duct tape, which according to 3M is polyethylene and I think this is safe in this context.