...the drain holes there are smart. I did make drain holes in esp the rear wheel houses (beneath the battery and AC drier), unless you make holes intentionally to drain the car holes will be created for you...
And on 8ma1046 and 1076, did have galvanic corrosion exactly in the area you mention (lower edge of the engine covers, where the aluminum is crimped over the steel frame). DeT used copper rivets when fastening Al and Steel together (ex, the noise covers over the engine and the intake inlets between the rear inner wheel housing and the paper tubes...). But otherwise, the prevention is to avoid the electrical connection -- esp, paint on the steel and tape between the steel and aluminum, so they electrically are isolated. And of course, maybe only available when replacing new AL.
While you have the chance, cleaning out the inner doors, making a swimming pool internally with POR-15, then drilling drain holes for water to exit are smart. The goose is something like a roach motel for water (easy to come in, hard to leave...)--Lee