After looking at ways to mount a phone on my GTS 300 I found a suitable water-resistant holder / cover (not water proof!) unit for $12 on eBay.
This unit had a clamp that would adjust down to the mirror stalk. To increase the stability of the unit I put a long self-tapping screw through the case and into the swivel adjuster plastic moulding, and another at the bottom of the case to a 3mm rivet nut insert that was put into the plastic just above the engine kill switch.
For navigation I used my Samsung S5 phone which has a GPS receiver in conjunction with a navigation application for Android (or Apple IOS) by the name of ‘OsmAnd’ which does not require a mobile phone signal to work. This uses the ‘Plotaroute’ GPX file information which VCOM uses for run planning. OsmAnd can also be used to give directions to a street address etc, and if you have a Bluetooth helmet headset it also will give you voice prompts. More detail is in the article I wrote for the MX5 club of Victoria on page 30.
To allow the phone to run with the navigation screen constantly on without running out of battery I bought an 8 amp hour battery pack and right angled USB lead which fits neatly in the phone holder with a bit of foam padding between the phone and battery pack. I decided on a battery pack instead of adding a USB socket on the scooter.
Hope someone finds my notes of interest. – James Lang