I have done this too. Got a ignition switched feed from the back of the light/fogs switch so the RA is activated when the ignition is on. Connected this to a ciggie lighter socket which I fixed behind the dash, there is loads of space for this. Plugged the RA in, fed the wire past the fuse cover panel (TORX bits required for this), then ran the cable around the dash. No rattles, squeeks or visible cable. Easy..
Good Luck