Dear BruceC2C,
You don't mention what the zippers are made of, are they metal or plastic?
I can only provide anecdotal information, but I have a Scott gear bag my bother bought for me as a Christmas present 30 plus years ago. I had a Chevy Avalanche, and like all Chevys, it was pretty much garbage. The weather-proof lid cover leaked miserably over the Winter and every single zipper on everything in the bed of the truck was frozen solid, tighter than a frog's butthole. I was sure my Scott legacy gear bag was trash.
I sprayed everything with WD-40 and worked the zippers back and forth until everything worked on every bag and case that was stuck fast. Then I washed the cloth stuff in the washing machine and once dry soaked an old t-shirt in WD-40 and wiped every zippers down. Ten years later they all still work!
I'd be more concerned with windblown sand getting in a zipper around saltwater. Silicone gel or spray should keep the zippers working, as long as something doesn't get into them and mess things up.
Regards,
Tim Murphy 🙂