You can get the Garmin units almost anywhere, most big box electronic stores will carry them, as well as
amazon.com
I bought mine at
amazon.
It mounts easily on the windshield right under the rear view mirror with a very strong suction cup arrangement. The power cord plugs into the mount and on the SP340 it is removable (on the SP330 it is attached and you have to take the whole mount off). The unit have its own internal battery but will power off when the ignition key is off. (unless you let it run on batteries). The GPS unit clips to the mount and removable with a quick release.
There is also a dash mounting plate provided. I am not sure if you can put it on top of the odd shaped instrument pod of the Rav 4 forward of the driver; but placing it on top of the air vents/ radio would be too far to reach. The under the mirror position works well and does not block the view significantly. (not legal in CA) The rear view mirror also shields it from direct sunlight glare on bright days. Unfortunately for the Rav, there is a patch of dot pattern paint on the glass directly forward of the RV mirror preventing you from mounting the GPS higher.
By the way, the GPS unit is very easy to use right out of the box and I have not bothered to download anything from their WEB site yet. I used to have GPS units connected to Laptops and PDA's but they do not have the 3D mapping and voice prompts. These Garmins access the satellites really fast, even sometimes in Car Park structures and thru tunnels; amazing.
It did go blank and erractic a few times driving on backroads in the mountains; but I think there is a Topo Map package that you can buy. The preloaded street maps are terrific for most towns and cities.