As I understand it, the process was;
Seam sealer over the bare metal (not a particularly good idea- as rust formed beneath the seam sealer). Depending on the level of restoration, some choose to remove the old seam sealer, treat the bare metal & reseal.
Primer- red oxide @ San Jose (or a close derivative using scrap/surplus paints). Rustoleum works well, looks good, easy to apply- brush or spray.
Sound deadener- as Jeff described above.
Neil