A good battery tender will be smart enough... I've had my car sit for over a month on a tender, and I know of owners who do the same with their airplanes
I vent mine on landing, maybe it's hooey, but it sure looks like steam with crap coming out. I'm running Exxon Elite.
I've read some guys take a hair blower (non-heat-low) and back blow the crankcase out of the open oil filler through the vent tube. That's a little anal ....
I am looking into engine dehydrator's or maybe going to build one. We get 100% humidity down here sometimes.