Those hides are too big. You want something that your snake can curl up in a ball and be touching on 3 sides. I just recently tried to increase the size of my snakes hides because she was lifting them up when she got in a high coil, and she didn't like them one bit. I would try to find something much smaller, like not much bigger than the water bowl you have now. In fact you are going to have a hard time keeping your temperatures up so you might try two hides about the size of the water bowl and a bowl about the size of one current hide.
Yeah just make sure the rat pup is as big around as your snake.