I am moving my instruments to another location and this is leaving rather large square holes in the GRP. How is the best way to fill these holes? Thanks in advance.
Fiberglass Boat Repair and Restoration Manual To Download
West System produce a fibre glass repair manual which describes how to fill holes amongst other matters. The methods are applicable to other glass fibre products, not just West System.
Its a good reference source and can be downloaded from here (link to down load is at the top of the page): -
I found a local catamaran manufacturer who had large thin GRP panels with gel coat from the window cut outs going spare and they were glad to pass them on for some 'tea money'.