We recently successfully, potty-trained our son and thought we d share some ideas on the subject. Type II SMA, and sits well unsupported. It took about 2 months. We had had a couple of unsuccessful attempts before, but got serious this summer - only 1 more year till Kindergarten, after all. Disposable diapers don't feel wet, even when they are.
Cloth diapers do.
Also, having him in daycare 1 day a week, he saw other kids going potty. Johnnie's' real treat was being allowed to pee in the grass this summer. This really seemed to help - the pleasure of admiring his pee. Now he likes to pee in a styrofoam cup, if we are out of the house. Enticing him with candy didn't work at all - it's hard to get him to eat at any time.