Re: new decking over old decking?
I just got done with this project on my 88 Four Winns, I had done a partial repair a few year earlier but the full extent of the rot became apparent back in 2005, so I cut out the old floor, had the 'glass shop do the stringers for me, and installed the new floor myself. Big job but you have something that will be better than 90% of the older boats out there, unless they have been stored out of the rain most of their lives. Don't bother with a band aid lay over job, it's not going to do much except make it harder to fix it right, or pass the problem onto some poor guy in the future......
BTW, on the topic of construction, I have been told that the old fashioned wood n glass construction, properly done, will be superior in some ways to the newer composites that are hyping 'no wood', the guy who owns the boatyard I use tells me that the newer boats don't ride as well and the glass is thinner.