Well you should probably change the width and height to .2, .2, because you're rendering a lot of it off screen with your X position at .8.
Using that method should make it resolution independent, if by resolution independent you mean it's the same percentage of the screen regardless of resolution.
However, a better way to do it might be to render that camera to a texture and render that texture on some geometry that has a fixed aspect ratio, so you don't have issues with rendering the game at different aspect ratios changing the aspect ratio of your interface controls.