I should mention that our main GPS sensor and the AIS GPS sensor, both from B&G, came with big warnings that these should not be installed up the mast. So both were installed at deck level.
Incidentally, I recall noticing that Amel is now installing what look to be a couple of GPS antennas on deck, forward of the pilot's windshield. I saw this on either a '64 or a '55 in La Rochelle.
Along the same lines, the Amel-factory Furuno heading sensor that was original to #350 sat at nearly water level in the forward closet opposite of the head. We now have replaced it with a B&G heading sensor sitting in the same little shelf.
Finally, the original Amel-factory Raytheon/Raymarine heading sensor is still outboard of the dining table, behind the seat, and just aft of the air conditioning vent, i.e, just above the waterline. It works very well and still provides reliable heading to the Raytheon autopilot.
SM2K Nr. 350 (2002)
At anchor, Spinalonga, Candia (Crete)