Ab workout for business traveller

Ok, I have started and stopped exercising so many times, I have lost count. I travel every other week, and life on the road is a challenge. I have rebooted c25k for my cardio, but now want to do something on the other days. I cant always get to the gym, and I am not ready to start with bands yet. I would like to focus, slowly, on my abs. Does anyone have a beginner ab workout that I can do in my room, that I can alternate or mix up? I want to be able to add to it, as my ability and flexibility increases. Any and all advice would be appreciated....heading to the airport soon :)