Gotta side with Rodger here and say take the baggie when going from one temp to another.





I spend a couple months traveling around to climb every summer and have been several places where it's reasonable to expect summer to blizzard conditions in a single day. If I have room for the camera stuff, the body goes into a ziploc with a couple packs of silica gel (if you don't have any, I highly suggest getting some) and the lenses go in padded pouches with another pack of gel.





On another note, going from 20 --> 30 degrees isn't really much of a swing and probably won't cause issues. However, if you're going from inside to 20 degrees in one shot, then you might want to worry a bit.