I haven't used this polish but the info sounds right for the Eriba GRP roof.

http://www.amazon.co.uk/Superb-Meguiars-...iars+wax+polish

Product Description
It may not have occurred to you to wax your boat, but it makes a world of difference in the long run. The fibreglass hull is covered in a gel coat that can oxidize just like your vehicle's clear coat. The difference is that the gel coat is constantly exposed to water, oftentimes salt water. Oxidation results in a chalky white residue within the gel coat that makes the hull look dull and neglected. This effect can be prevented by applying a quality wax like Meguiar's Mirror Glaze #56 Boat/RV Pure Wax. There is a difference between car wax and boat wax, so use one recommended for boats. Meguiar's #56 Boat/RV Pure Wax is designed specifically for the protection of fibreglass and all painted surfaces. It is made of pure Brazilian carnauba wax, silicones, polymers, and resins to provide extraordinary gloss and long-lasting protection. Resins allow the wax to bond to the gel coat in order to withstand the friction of the boat cutting the water and salt. The carnauba creates a beautiful shine and slickness that allows the boat to glide through the water with less resistance. As with any wax, Meguiar's #56 Boat/RV Pure Wax will protect the boat from UV exposure, salt, and rain. Painted hulls will remain bright and resist the signs of age.