Theory
I don't think were you live has too much bearing on the corrosion inside the engine. The moisture comes from the fuel which when burnt makes mostly co2 and water vapour.
Some of this gets blown by the rings into the case and now you have an engine at say 180F full full of air that is close to saturated (100% relative humidity). As the case cools to the dewpoint of said air (lets say 150F) the moisture starts to condense on the metal arts inside the engine.
My second hypothesis is that a lot of the moisture gets blown out by the airflow from the dehydrator before the air has a chance to condense.
My homemade (non recirculating) system pumps into the breather tube and I crack the dipstick to let it vent. When I first hook it up I can see a column of steam coming out of the dipstick tube.
As to which way is best is hard to say. Mine has a free flow into the breather and out the filler. But because it doesn't build up any pressure, none of the dehydrated air gets pushed up into the cylinders.
I think if the cylinders are steel it would be better to have a pressure system, but then you are not getting the free flow of steam out of the filler tube, and all the dehydrating has be done with the dessicant.
I think you'd need some controlled experiments to determine the best way.
My guess is any dehyrdrator is better than none.
Frank
