Hook train him. I was told that for my burm. When the top opens and a hook comes in and lifts his hide and pulls him out, it's handling time. When the tub lid is opened and no hook is there, it's feeding time. haha
Plus you can't expect an animal to just be all nice when the only time you open the tub is for food. Of course he is going to to think opening of the tub is food.