Bus from FRA to K-town (commonly used reference by Americans for Kaiserslautern, not KS) can be found here:
www.delux-express.de
Train is fine too for around €30-€40 one-way, but will require a change in either Mannheim Hbf or Frankfurt Hbf. Not so fun with a lot of bags, but is 1:30-2:00 travel time.