I'd install it and wire it as directed in the instructions, EXCEPT, the line they say to connect to "reverse", I'd connect to the glove box power lead or the cigarette lighter power lead, those come on with key.
In this way, it would come one and stay on anytime the key is 'on'.

There are other options, you could use one of these fuse taps and take power from the switched radio fuse in the fuse box under the hood, drivers' side. YOu can get them at any auto parts store, they call it a "fuse tap".






The radio has two fuses, one is on battery, you don't want that - the other is on switched power with the key. Using a stiff rod, you can fish the wire thru the back of the fuse box, and it will come out behind the little door on the driver's end of the dash -where the fuses for all the lights are. This is the "Illumination Control Module". (DO NOT try to use any fuse in THAT box, they are energized by the light switch.)