Ditch the factory radio and put in a decent aftermarket.
Running the wires is not too difficult. Often what installers do is find the factory wire colors by pulling out the speakers and then find those wires into the car. Rears are VERY easy. Front kickpanels not so bad either......... tweets more work but all inside the cabin. No need to run into the doors.
Aftermarket decks come with a cage that mounts into the DIN hole. The deck then slips into that cage and locks. The cage has tabs you bend into the back side of the dash and usually a mount off the back of the cage that you can use if you want to. It's rather easy stuff to install.
Hope this helps.
Current : 2013 Mini Countryman JCW, 2007 Z4M Roadster
Past: '88 E30 M3, '69 BMW 2002 Ti, 2000 328i, Audi A6 TT, BMW X5 3.0i , Audi A4, Mini Cooper Clubman S 1.8T