Heat & liquid naturally make o-rings swell. My husband has a kit of black o-rings here at the house (like 20 different sizes), & recently recommended the "green" o-rings to me, because they are more heat resistant. I think they are called "high temp O-rings". I picked up a box with about 20 different sizes on ebay. It's always nice to have several sizes of o-rings at home. I use them on lanyards, tanks & some mods. I don't think that storing O-rings in your climate would pose a major problem though. They have a tendency to swell when completely saturated in juice is what i've found.
Long term for your Ego Batteries.........I was gonna say buy either the silver or gold colored ones, & not the ones with that soft coating. However I see that you already have a large Ego stash. I'm thinking the clear nail polish is gonna suck, as I know that my nail polish only goes 3-4 days without chipping. I'd go more with a "Sculpey clear coat", (clear coat for polymer clay). Coat your batteries, let them dry, then go ahead & do another coat. It's not like you will be putting that part of the ecig in your mouth.
reminds me::::my husband once went to the store with a hello kitty bandaid on his finger, & used my pink baby phat visa to purchase something. yep, he's totally secure in his manhood
