Glass-reinforced plastic, but more commonly known as glass fibre (not fibreglass, which is a trade name). Used by most motorhome manufacturers, for everything from bumper surrounds to side skirts to complete bodyshells
Found on http://www.encyclo.co.uk/local/20699
GRP refers to the type of materials that the Laser II hull is made out of, it means that the hull is made out of combination of fibre glass and plastic. (GRP is short for Glass-Reinforced Plastic).
Found on http://www.jard.co.uk/laser2/glossary.shtml