spray with WD-40

Coat it candle wax

Ive used both above mentioned. They work too. But if you are already out on the water and have neither, use the water coming out of the motor. It's usually warm enough to open it up especially if they are plastic zippers. Hope this helps

rub a bar of soap on it, any old cheap bar of soap works and its dry so it doesnt get in to the container or stain anything

its cheap, its easy to keep in the boat for on-the-water touch ups, it cleans off the salt residue, and it keeps the water out and repels the salt

Wax is the ticket. They have blocks at Walmart. Good for melting down and pin-feathering ducks too.

Vaseline on your finger and run it down the length of the zipper-- it will repel water and they will not rust!

Yes sir, the Vasoline is what I use. 1 or 2 X's during the season and then a coating before storage for the winter...works like a dream