Chris, take a look on Hodge's postings (from memory) as he has a remote face UHF with the face set at the front of the centre console and strapped down with zip ties. Great photos of setup.
I copied that set up and it works a treat.
Brought the cable through the firewall by coming through beside the air con drip hose (it will fit through the grommet but be gentle as it dislodges easily). Pulled the hose back into the car, brought the cable in, then pushed the air con hose back through.
Main unit is under the passenger seat at present as I haven't got around to finding a better spot.
Mine is a 2012 d22