Wouldn't it rattle and move all over if you just let it lie in the bottom ??

I like the idea of mounting to the side ... that way it is not that wide to block the entire area ... so you can still keep something in that bin
Otherwise you can't put anything in it, since you have to put it on top of it.

 

Just stick some velcro on it (at least temporarily) and see what works best.

 

Here's some shots of how I mounted it. The dealer can install Sirius and replace the XM unit so you can control it through the AV unit, however with the merger and loss of Nav traffic, I figure I'll use this temporary solution until I hear how the merger plays out.

I installed it myself, took about 30 minutes, almost the whole time was nicely running the antenna, as you can see from the pics, I ran it from the top of the trunk, and kept it on the trunk and ran it to the left hinge where all the other wiring is, then ran it through the ski pass through, under the drivers side rear seat, along the moulding of the drivers rear seat door, then passed it under the drivers seat and mat and up through the console. It's easy.

The unit just sits there, it's perfectly sized that it actually locks into place tightly, when I push the buttons it doesn't rock or anything.

Edit: Wow the car's dirty! lol