I did this mod but went with a different method mounting it. My main goal was making this extremely easy to remove since I plan on using the tablet a lot out side of the car as well as in the car. Ended up getting the Scosche SU2027 to decrease the size of the hole left by removing the stock Nav Unit. Mounted the snap on back case with double sided industrial velcro (very strong).
Here are some pics:
Without the Schosche SU2027 (looks like crap):
After installing the Schosche:
Side view (need to trim the velcro)