This is what i've always done.
Most people will use a relay. SPL-Lab SMART Voltmeter has built in relay in case you have this installed.
Anyways, installing relay, etc, the 12v constant power line should be fused for proper wiring.
The fuse for this relay, i keep right next to the fuse panel under steering wheel.
You do not fuse the output (remote wire), you fuse the 12v+ constant power line feeding the relay (same way with SMART Voltmeter as well).