The seat cushion boards on my 2004...

[Zack]

The seat cushion boards on my 2004 270 Sundeck are Low Density PVC.  Several are broken and before I replace with the same thing I wondered if anyone's found something that's still lightweight but stronger than LDPVC.

[wingless]

Why not use marine plywood, covered w/ epoxy?

http://plywood.boatbuildercentral.com/

[Time_Well_Waste]

Better to use King Starboard.
http://www.boatoutfitters.com/king-starboard-cut-to-size.html

They will sell you just what you want.