If you treat your frame well and wax the paint then rust is not a concern. My 14 yr old mountain bike has perfect condition tubing(I checked) and I had it 6 yrs on a pacific island before coming to eastern pa.
The planes I restore as a job are the same steel tubing and are on avg 50 yrs old. Since they treat them, we rarely encounter rust. There are a great many treatments out there now to choose from, but almost anything works.