I agree that you should automatically take him out when he comes out of the crate and after meals - we did that too. Along with tons of praise and treats.
We opted not to allow accidents to happen un-noticed. Whenever Bailey was loose in the house, she was in a room with us, all exits and hiding places were blocked and she was monitored at all times. Whenever she squated we were there immediately to catch her and correct. She learned to ring the bell at the same time.
We dedicated two solid months to the process before we eased up. I believe that was why we were so successful.
Oh, yes, there was bell abuse when she was younger
but after the first year, it got a lot better.
Good luck!