The crank arm corrosion is a byproduct of galvanic action
where two different metals are touching in the presence of moisture. Salt water accelerates the process. In this case where you have stainless steel and aluminum, the aluminum corrodes.
The best way to protect the aluminum is by adding a third metal such as zinc. The zinc acts as a "sacrificial annode" and will corode instead of the aluminum. Fortunately zinc is inexpensive and very common. In fact, any 1983 and newer U S cent is 97.5% zinc.
Look for a worn penny where the copper cladding is mostly worn off,
bend it to fit in your pedal shaft and slide it in.
BTW, the crank arms are now anodized for better durability. They used to be E coated (painted). Between the improved crank arms and one penny fix (check it annually for replacement), you shouldn't have any further problems.
PS. I checked out the drums. They do have a drain hole:
But the hole doesn't drain completely (residual water is highlighted in pink):
So it is best to rinse turning the Drive upside down a few times to purge the salt water (which also leaks into the shaft of the crank arms).