Some I have read are concerned about winter storage and mice getting in the exhaust system. Suggestion on other forums is to use steel wool to block the exhaust. I found beer cans fit nicely, they are aluminum so won't be an issue as steel wool can rust if there is any moisture. My winter cover nicely holds the beer cans in place so the little critters can't work their way into the exhaust. If you didn't have a cover probably could find something else that would hold them tight. The exhaust narrows once inside the tips so the cans close it off completely.