A hatch made out of fiberglass (instead of acrylic glass) has surface that isn’t 100% plane and the suction cup will have problem to stay put for a long time. It will leak in some air. To solve this problem we need to mount a small plastic plate with double-sided tape. It’s the kind of plate used in cars when you mount a GPS to the dashboard. This plate is sold as an accessories #1542 Plate for fiberglass hatch.