Dug out some failing seams, taped the edges, put in SIS-440, used a putty knife to level the surface, and removed the tape before the caulk setup. Got a great result. The SIS-440 set up fast, stuck well, and seems the perfect durometer for a deck joint--not too hard or too soft. The color also matches the existing caulk. It's also priced under $15/tube. What's not to like?
I bought this tube last winter and it summered aboard in the southern Florida heat. Amazingly, the tube was still good. Clearly, shelf life isn't a big problem.