Here's my setup. The textured plastic cover above the radio is completely removable. It is held to the dash by four screws. I removed the cover to drill the holes in it and to attach the bolts through the cover. When putting the cover back in place, I was able to run the GPS electrical cord behind the radio and down to a 12v outlet for a nice clean look.
As can be seen, the cover is hard plastic and in one piece. If the Garmin GPS is ever removed, I can leave the bolts in place to fill the holes or I can easily purchase a replacement cover from Winnebago for not much cost. Works like factory for me, others may not have the same advantageous situation that I have.
2010 Itasca Sunova 33C, (lots of upgrades and modifications)
2011 Honda CRV, 2004 Rubicon (many modifications)