You're covering the entire camera in a bag, all the time right? Literally, I would not use a camera in this environment for a week unless it were semi-hermetically sealed. This kind of stuff:
You're probably better off using a 645 format and 220 film rather than 120 and 6x6/6x7 as it's less reloading (30 frames vs 12/10). I'd keep a plastic bag around it at all times and change film when reasonable.
Stop worrying about grain, resolution, sharpness, and everything else that doesn't have a damn thing to do with substance.