Weathering styrene to look like wood

I have started to build Walthers Pier kit. I would like the pilings and the remainder of the wood on the pier to look weathered like they have been aged by salt water. Any suggestions. Also do you prime the styrene before painting.
Thanks to all those who respond to this.

I have a web article about weathered wood and styrene at:

http://www.pacificcoastairlinerr.com/weathered_wood/

The first three boards are styrene

Hope that helps
Harold