My Home Depot has both small tubes and calk tubes of slow and fast.
Also, my Ace Hardware has calk tubes of slow, and small tubes of fast.
I've been told by a boat builder that the fast stuff is not nearly as strong. If you have the time, you might consider the slow stuff.
*EDIT* Oh, and where are you using the sealant? Are you talking destroyers just to seal the holes? Or you talking the foam backed ones like Macc's older tubbies, Tom21's? If you are talking gluing those type on, epoxy and thickener ONLY. You could not pay me to use 5200 to glue tubbies on...maybe on a ski I didn't care about and I want to remove them eventually. I've not seen it turn out to my liking.
If foam backed ones, you can get away with adding some pigment to your resin if you need it to match a black bottom. Cabosil will make your epoxy white for a white bottom ski, and if you run your finger around the squish out, you will end up with an almost invisible line.
