You might have too much oil down the bore. A light coating is all that's needed. Additionally, make sure the bore is 100% dry before you oil it. If not some of the moisture will get trapped in there.

I've owned several Genesis' (both blued and stainless) and I have not had a problem with rust in any of them. One of which was one of the first ones that came out. I could have been that it was loaded that long or moisture got in there that you were not aware of.

Try the JB Bore Paste as suggested. It should clear it up.