Galvanic corrosion, as I understand, happens only in the presence of an electrolyte. Stainless fasteners into aluminum in marine applications is a bad idea.

But what about in non-marine applications? For example if I wanted to build an aluminum-framed camper trailer clad in stainless sheet and fastened possibly with aluminum rivets and/or stainless screws and/or common steel bolts, would corrosion be a concern? Say it was stored outdoors, exposed to normal fresh rainfall, not near the ocean with salt spray. I realize fresh water is an electrolyte (esp with natural atmospheric minerals) but is periodic rainfall exposure enough to be of concern?

 

Up North, it is quite common to replace plated steel fasteners (screws) holding inspection plates on small aircraft with SS fasteners. OEM plated screws rust, particularly if the airplane is tied down outside, and can be very difficult to remove. SS screws avoid that problem. I have never seen any adverse effect on the inspection plates. Of course, aircraft kept outside in Florida all have corrosion with or without SS screws. It can be particularly bad in aircraft that have magnesium skins on the tail surfaces to save weight.

 

Example of aluminum-framed solar panels SS bolted to Stainless UNISTRUT channel exposed to PNW rainfall over the years. The structure is regular UNISTRUT.

A lot more algae growth than metal corrosion.

The original array structure started in Apr 2010 with rubber isolators between the aluminum panels and mounting tabs on regular UNISTRUT for the middle panels.

 

Anytime you have a current flow, moisture, and different metals you have electrolysis. This can appear like corrosion as one metal gives up it's electrons.