I had a S.S. Fixed-Frame Bimini (2/3 length) fabricated and installed on my GW225T over in Phuket Thailand last year.
Instead of using Sunbrella for the top, I used "Nylex" from Australia, which stands up to the weather much much better than Sunbrella.
For the side and back panels, we used "Cool-A-Roo", which allows the boat the breath....not trapping any moisture inside.
Have a look at the Grady Forum......Tips, Modifications.....2008 GW225T Refit in Phuket Thailand. viewtopic.php?f=3&t=19673