In general, any GPS should be located where it has a clear view of the sky for best results. Orient the Carloop GPS face-up for best results per the design guides.
Metal is great at blocking signals. So, if you use a metal box, you can be guaranteed that you will not receive signals. You can experiment with paper (cardboard) or plastic boxes, but avoid metal or any material with a metal film or liner. Metal parts of a car will block the signal also.