Just a little FYI I thought I'd share. I always buy caulking/sealer in the large 10.1 oz (300 ml) tubes, whether it be for home or the boat. After a few times of loosing half a tube, or more, after letting it sit over time, I've come up with a method to preserve it for quite a while.
This picture below is of a tube I've been using for over a year now and is about half done. The last time I opened it, before today, was in Oct. 4 months ago. It had only hardened about 1/4" into the nozzle and was completely soft otherwise.
What I do after use is make sure the snap-on cap & nozzle is clean before assembly. Then I install two little condoms (from the hardware
stores) and the put it in a 1 gal. ziploc bag. I squeeze out all the air, seal it up and the wrap tape around to hold it in place. Then store it in a cool place. In the bilges of the boat seems to be fine.