In practice you are unlikely to get any problem in this application with Stainless fasteners of a suitable grade:

A2-70 stainless is 85% tensile strength of 8.8 steel, A4-80 is 97%

Useful Stainless data here - http://www.anzor.co.nz/?t=30

It's not a safety critical application (unlike suspension or brake mountings) so if for some odd reason you do get a failure it's not going to kill you