If there's a spare fuse slot, use that and use a relay switched by the reverse lights to switch it.
30/87 should be the reverse feed through the relay... Probably from the reverse light fuse listed.
Are you saying I should mount a relay somewhere, feed it 12v from fuse 28, and activate it with current, also from fuse 28, and fed through the reversing light switch?
Nothing of the sort.
On the rear SAM identify the following...
1. An empty fuse, ideally ignition fed.
2. An empty relay spot.
3. The supply to the reverse lights.
Connect 1 to pin 30 on the relay, pin 87 then feeds the supply to the parking sensor unit. Ground from the parking sensor unit completes this circuit.
2. Is a cosmetic luxury, you can duct tape the relay in the glovebox for all I care
Obviously don't do this.
3. Confirm that this is the power for the reverse lights... Looking for continuity with ignition on 2 and reverse selected. Two torx screws and some clips free the tailgate trim.
Once this is confirmed, cut this wire. Attach one end to pin 85 on the relay. Connect the other end to pin 86 on the relay.
Can't make that much clearer, but Dave or Nick may have more to add