I mounted a Garmin GPSMAP 176 using a SlipStreamer universal mount and the upper part of the marine mount that came with the GPS. I also replaced the stock 12v receptacle with a Marinco weatherproof locking plug/receptacle combo...the plug locks in place so it won't vibrate out.

GPS picture

 

Sounds like you are putting together quite a nice machine. I just purchased a set of Garmin Rinos for my two machines. The peer to peer feature should help when separated.