I flew 1600 hours in my RV6 with stainless screws holding the tanks on.
The plane was painted for half that time, so they where not in direct contact with the aluminum for half that time.
Light aerobatics up to 4 g, nothing broke, did not see any corrosion issues.
They do tend to gaul and cause problems when removed, I will be lubricating the threads on my new RV7, Iwill be using stainless