My voltmeter is weatherproof with leads sealed coming off the back - yours does not look like it is weatherproof - if not, then you need to keep it dry - which could influence how you mount it and where.
Be sure to 'tie' the voltmeter into wires that don't have too much of a voltage drop back to the battery - this was not a problem for me as I installed a HOT fuseblock (for other reasons) to the front of my SWing fed with 10 gauge wire.
I was surprised to find that my voltmeter gave me no indication of the percentage of charge my battery had as when I turn on my key the lights draw so much amperage that the voltage drops in the 11s volt range - but the SWing starts fine.
Where I like my voltmeter is when I am riding I can see how well my stator/alternator is charging the battery - and if I am using power faster than it can be replaced. This is important when I am using heated gear as I can overload the system - but can cut back on load (load shedding - such as turning off the high beam or turning off a piece of heated gear).
If I did not have 'auxillary loads' on my SWing then the voltmeter that I purchased would have been, for me, a waste of money. The stock SWing has ample power (450 watts I believe) to power everything on it - plus quite some more - so that measuring voltage all the time is not necessary - interesting but not necessary. When the system fails - battery, alternator, stator, etc - you are going to know it and no voltmeter installed on your SWing is likely going to help you diagnose the problem or keep you going - you are just going to have to fix it.