I've always kept a foil tray of charcoal in mine. I really don't like leaving them open, since it puts a strain on the hinges, albeit small. The charcoal does a wonderful job of absorbing any moisture in the unit, and I burn it with my first campfire.
Bear in mind, my units are older, and I have to do what I can to protect parts that may no longer be available!
Tom - Retired OTR 20 years 2 million mile club - 1984 Diamond Maxi
I love everybody! Even some above ground!