I live in Georgia, which gets very hot and insanely humid. To prevent condensation, I throw my gear in the tunk a little while before leaving, and I leave the bag unzipped with the locking straps holding the bag closed, that way warm air can enter the bag at a slow pace. Another option would be to set the bag outside for a while before leaving, partially open, then zip up before departing. You want to let the camera and film slowly change temperature. Keeping the gear in ziplock bags is not such a great idea, except for the film holders, I keep mine in anti-static (ESD) zip lock bags, primarily to keep dust off of them.