Howard I'd assumed that reducing relative humidity would reduce corrosion whether through raising the temperature in the body of air or by removing moisture with a de-humidifier.
Relative humidity is just the percentage of moisture in the air compared to the maximum that it can hold at that temperature. Given that the maximum goes up with air temperature, so the same amount of moisture gives decreasing relative humidity numbers.
My guess, and it is only a guess, is that data on a bridge isnt very relevant to a car in a garage. With the bridge you will get condensation at times when the bridge structure cools overnight, something that I have never had happen in my garage. And guessing further, II suspect that water droplets on some steel will have it rust quicker that moisture in the air.
All educated guesswork at best!
