If you are landing 180's consistently try doing them blind its not much harder it only takes a handle pass. These are good practice for learning to pass the handle for 360's. BTW blind is just spining counter clockwise if your are right foot forward oposite if you are left foot forward.
If you want to learn an invert. Try the backroll first. It is the easiest vert to learn by far. Just take a strong cut in heelside, charging the wake is key. Wait for the pop and then send the tip of the board up and away from the boat and look over your back shoulder to help the rotation. You will eventually come around and land (hopefully). If you have problems with this type of backroll try doing it mexican style. Its just like doing a front flip on a trampoline. Just hit the wake hard and then throw your head down between you legs and kick your feet up and over. Keep two hands on the handle the whole time and you should be sticking the landings in no time. Hope this helps man.