Is the anything that can be used for dry exhaust flappers. I'm thinking the rubber ones I had before are going to melt with no water in the exhaust

nothing if your totally dry..

Maybe have some stainless flaps made you see on over the road trucks and construction equipment. At idle they might make a ton of clanking noise but I really don't know. The ones from Rex will work fine even after the rubber is burned out:

http://www.hardin-marine.com/p-12580...-flappers.aspx

http://www.rexmar.com/page230.html