Hightower
Try
http://www.solentplastics.co.uk/ and follow the products link, and then marine.
I don't know if this will be of interest to you, on my boat I use removable dry boxes. They are not fibreglass, but they are tough plastic and fully waterproof, Ive been using them for four years now without breakage.
You can also remove them at the end of the day and stack them in the back of the car so bits don't get nicked at night etc.
The last time I ordered some they were £22 each, and come in many colours.
They also do various other enclosures/boxes etc - may be worth a call.
Hope this helps