I am thinking of adding an insulated, permanent cover to my permanent pier. A material that I am considering is extruded polystyrene (XPS), 30 mm thick. It seems to be easy to work, reasonably rigid and to have good insulation properties.
I am thinking of a 900 mm x 900 mm x 600 mm box, glued with silicone sealant. I would probably cover it with reflective insulation secured with contact glue. There would be a suitably sized plywood base on the pier to fit it to.
My question is, has anyone used this material for this purpose? If so I would be interest to hear any thoughts.