Even if it was low-grade sheet steel, I wouldn't expect it to rust (visibly) unless it is taking you a long time to build this chassis - or where you are working at is very humid.
Forgot to write that it's steel sheetmetal. And yes, my workshop is ridiculously humid. Will any primer do? (thegeekway mentioned etching primer) or is there a special primer for steel that I should know about?
EDIT: Found some at homedepot. Thanks for the help everyone.