I live in a very humid, salty environment. We don't buy nice vehicles, or nice appliances. In five years, this is my third computer, for example.
My workshop is a tin garden shed in the back yard - a rusty one
It was with much trepidation that I bought myself an oxycon last year, and am paranoid that it just won't fire one day. It will be a case of simply chucking a thousand dollars down the drain.
The kiln I use is an old brick ceramic one with an analogue sheathed probe pyrometer.
When I first got it, I was covering it with a plastic BBQ cover to keep the moisture out. I learned that this was making matters worse, encouraging more condensation, rather than less. So I don't cover it up at all, now, but keep the door closed once I've harvested my glass. It's still around 50 celsius when I do that, so still nice and warm and dry.
What happened while I was covering it was that the condensation would occur in the power housing, not the kiln itself. The safety cut out would kick in before the switch was even fully engaged. The electrician we got out to look it over said that it wasn't being damaged (any more than any other damage that salt or moisture does), but just doing what it's supposed to. If I needed to use the kiln, and there was condensation, I'd have to sit a fan in front of it to try to dry it out so I could get it going. Gah!
As for the oxycon, I do cover that, but only with breathable sheeting. The last thing I want in that is condensation either.
So, if it's humidity you're worried about, by all means cover it, but not with plastic.