The reason cedar doesn't decay is Tannic Acid. It
is a very corrosive acid. When mirco-organisms try to eat the
cedar the acid makes them stop and go away.
This Tannic Acid is will rust right through ordinary
steel or galvanized screws and bolts.
Don't be fooled with the term "Rust Proof or
Rust Resistant Hardware".
If the hardware isn't stainless steel it will rust.