The same as most things, as much as possible.
Not very constructive
For example, do you want to use it regularly for full-on proper ‘Off Road’ navigation? If so, your Nav V (whilst still a very good device) might not be your first choice.
Similarly, you haven’t answered the reasonable question as to why you want to mount a phone AND the navigation device onto your bike. If it’s just for calls, you can channel your phone through the Nav V, meaning that you can leave your phone in your jacket / tank bag / tail pack.