Even then would the potential damage from a short time exposure to water be more damaging to the brakes than operating in a rainstorm or on salty, snowy winter roads?
Yes. Because during those conditions the parts are all moving. Parked not moving rust seizes and damages what it attaches to and surprisingly within a short period of time.
All I know is due to health reasons my MH sat just ONE winter in the driveway and calipers were first on the list to be replaced. Rust is something you don't just dust off and hit the road.
If this was a MH that the OP is considering buying I would advise NOT to. It goes well beyond just the brakes.