01marc: .....corrosion requires different metals and an electrolyte....
Electrolyte includes grounding a DC battery to the chassis. That's why they call it, electrolysis. Paint is not considered 'electrical insulation'.
OP, If you have Aluminum and have your heart set on using it, no worries. Your bus, your way. It's not gonna ruin everything.
"A man is worked upon by what he works on. He may carve out his circumstances, but his circumstances will carve him out as well."