Courtney Thomas wrote in message ...
What is the best material for fabricating a 'year round' boat cover for
an unsheltered 40'fiberglass sailboat that is hauled or moored in the
South ?

Durability, maximal UV resistance and breathability are among qualities
sought.

Suggestions/observations/experience regarding it's design and
implementation are also appreciated.

Disclaimer... the link I am about to give is a client, but in this
case it might fit the bill:
http://www.absoluteshelters.com/
Scotty