Thanks for your prompt advice. Much appreciated. I had come to the same tentative conclusion although, not being “over practical”, I was hesitant in reinventing the wheel if there was an alternative, simpler solution (often the case).
I have now looked at the references you gave and communications in respect of a similar previous enquiry. Only two further queries: (a) the polystyrene foam is encapsulated on two sides by a thin glass fibre wall/support. Presumably no choice but to cut this together with the foam and then re-fibreglass back as best one can? (b) any tips on cutting/joining the foam to ensure a solid bond – is there, for instance, a particular waterproof glue that expands to fill irregularities in the foam caused by the cutting?
Again – thanks for your advice. Mike