Composite Stringers in a boat

[skooter]

I have another thread on the DIY forum about rebuilding a duck boat. I have stripped it down to the fiberglass shell - which included removing the stringers and transom. I'm not worried about the transom as I have a good plan for it. However, I'm looking at how to do the stringers. I know that I can put them back like I found them, but I'm leaning to something that won't rot. Has anyone used the "foam insulation" board from the hardware store and then fiberglassed over it? I'm thinking that this would give me the structure that I need and definitely wouldn't rot.

Any other ideas?

Thanks,
Skooter