The real question is, how long do you want this paint job to last? Rust on flat surfaces can be addressed by sanding, but what a about the seams where adjoining panels meet? You can't get in there with sandpaper and using chemicals in these seams will leave residual nastiness that will come back to haunt you even with epoxy primer on top of it.
Sandblasting is the best solution for removing rust so that epoxy primer can do its job.
