I tried using a 7" tablet as a GPS last year, inside an Otterbox Defender, mounted using a Ram ball mount between the handlebars.. Works ok...to a certain point.
Here's a couple of things I discovered, and why I ditched it and went to a 7" Garmin Nuvi instead;
Regardless of which gps software I loaded, there were drawbacks. Old/inaccurate maps, buggy software, and...here was the biggest problem- does not work in areas with no clear sky or cell signal.
I went to NC last year trying this, and was sorely disappointed.
The Garmin Nuvi 2747 7" used w/ a Ram mount is a better and cheaper way. It works- everywhere.
Now, the challenge is how to waterproof it for trips...
I also moved it to the RS handlebars, with my Iphone 5s mounted below it. (Using a dual ball Ram mount.)
It's much more solidly mounted there, higher... which really helps me see it at an easier glance, which means I don't have to look down. Love the big 7" screen!
I can also plug in the coordinates in my Iphone's "Maps" gps, and get turn by turn via bluetooth.
I think it's the Nuvi 2797 model that has an "out" audio jack that you can plug a cable into and then plug into your G9X input jack to hear turn by turn that way. My model does not have that jack.
Oh, and Ram makes a great mount for these two Nuvi's. Very pleased with it. It allows for quick, easy install/removal of the unit. The electrical pinned base mounts inside the Ram mount. Sorta reminds me of the way the Zumo attaches/ detaches, except does not have a screw. I've got $230 total invested in this, and love it.
Just some things I discovered... the hard way.