Mercury - Top Mount Kit (GPS) SmartCraft / NMEA 2000 Mounting 98-8M6009518. Overview. A good GPS antenna needs a clean mounting point if you want strong, uninterrupted satellite reception. The Mercury 98-8M6009518 Top Mount Kit gives you a compact, stable platform for installing a SmartCraft or NMEA 2000 GPS antenna on the helm, hardtop, or console. It keeps the antenna elevated, secure, and positioned for the best signal, especially on boats where space is tight or mounting angles are limited..