Since I'm making one of these, I can help you out.
I'm doing it two ways, depending on the level:
1: No actual scrolling - the background moves instead.
2: Create a 'camera' object - I use a box - with a movement and center the screen on that. Move the box, and always move the ship the same amount as the box moves. I'm using private variables to store the X and Y position of the camera from the previous frame, and moving the ship the difference between the frames. Both RTS and bullet movement work great for scrolling.