Keep in mind that you may have more problems with your mags than your gun.
My 9000s has a polymer frame, and I have had relatively little problems IBW and especially OWB.
I will be getting the Crossbreed - with horse hide - early next year for IWB. My current IWB - DeSantis Tuck-This N9 - has no rusting problems (provided that you do not put your spare mag in it), though I have some other issues.
Any OWB will work, covering with your shirt out. You might find that better, unless you need to tuck your shirt in.
Mags - both spare(s) and in the gun - drove me nuts until I got some Leatherman Tool CORE or the SUPERTOOL (aka SUPERTOOL 200) ballistic nylon cases for the spares, and soaked all the magazines with Sheath Rust Preventative.