I prefer to sing in the shower vs. the car. The shower is just steam you know its just you and nature and no clothing. You know there's nothing separating you. It's just you and the voice - you and the water.
I think the biggest difficulty is that when I'm here in America there's a necessity of using English so I really have a great sense of really wanting to learn but unfortunately when I head back to Japan the necessity vanishes and so does my enthusiasm about learning.