I have found all kinds of stuff left in my Spyder.. Plastic squegees, a roller, plenty of trash from cutouts, glassed in cigarettes...
Anyway, I have used 5200 on hull to deck joints in the past, you just have to make sure you get it clean first. Not very easy. usually a hacksaw blade or a 3" cutoff wheel will get into the joint enough to clean it out if you use a few prybars to seperate a small area at a time.
Now, on my Spyder build this winter I will be glassing the hull and deck together and getting rid of the rail completely. I will probably start another thread on it if there is interest.