Hi David,
I had a winter cover made for Shemar when she was new in 2006 but it was made to cover the boat from bow to stern, not just the cockpit. It was made to order by C&J Marine Ltd of Clay Lane, Chichester, West Sussex, PO19 6JG, T 01243 785485, www.cjmarine.co.uk .
They came and measured the boat, made the cover in three parts to cover the bow then from the mast along the boom to the pushpit and a stern section to close off the stern, all sections zip together and reach over the guardrails. On completion they came and checked that it was a good fit which it was.
This may be rather more than what you had in mind but I have been very pleased with the cover which keeps the sun and rain off when my boat is layed up and enables me to work on her in the dry.
Kind regards
Martin
Shemar P335/46