Reverse Camera retro fit to an estate! Wiring Nightmare

[Tayto]

Hi all,
A relatively new Merc owner here. I have a 2012 C250 Estate. I am going to add a reversing camera, I've ordered one that replaces one of the number plate lamps but.....
I need to get power and different guides talk about tapping the reverse lamp cable, others don't. Some talk about relays others don't.
I somehow need to get the cable from the tailgate up and through the rubber cable feed at the top of the tail gate, then down to where the rear light cluster and fuse board is.... then I need to get a feed to the head unit. I have already installed an Andriod head unit that has rear facing camera connections.
My options are to route a cable all the way back but it would need to come up the passenger side? Or can I get a cable across the driver side? Alternatively, I can use a cheap wireless dongle set which would emlinate the second part of trailing a cable through the car but I can't find anything on anyone ever using this method.

I'm very confused as to what's the best solution here. Any one done this in an estate before or used wireless?

Thanks in advance

 

[Tayto]

OK, looks like it is the ugly route up and through the rubber cable hose at the top of the tailgate and down again.

Has anyone used a wireless set-up from here to the headunit? Do they work or do I have to route through the car like a standard installation?

Also - wired to the fuse box so permanently on or tap the reverse light wire?