PVC, stainless steel, aluminium, and gavanized steel for my wet and corrosive environment (sea water). Bell boxes hold up pretty well up here.
For the most part, the wettness I deal with is rain and lots of it so for the most part, it is non-acidic. The sea water is a whole different animal. The salt likes to eat ferrous metals if left unprotected.
Aluminum and stainless together is always bad news in an electrolyte like salt water. There is a teflon based goo you can coat the junction with that makes it better but eventually the stainless will start eating the aluminum.
Interesting topic, John, There is a galvanic chart around somewhere, I saw it some years back, it shows which metals will corrode when placed with other metals and to what degree, this is, I might add, first year apprentice electrical theory.
Having said that, I work in an environment (dairy sheds) where anything is either PVC, stainless steel or heavily galvanised steel pipe. Anything that even remotely touches concrete, is always stainless.
I remember back when PVC enclosures became prolific in the trade here, some you bought would last quite well out in the weather, some just fell to bits, due to the sunlight, thankfully most of them problems have since been ironed out.