Back panel not removable... any thoughts to install a magnet plate?

Hello, folks.

I've been a big fan of magnet car dock since Nexus 5 had magnets on its back. As I've been using LG G3, OnePlus One, and Note 4 (N910T and N910S), I attached magnet on its battery (or back) cover to use my phones with the magnet dock. Unfortunately, it seems there would be no way to remove back panel for Moto X Pure Edition unless teardown major components.

Would there be any ideas or thoughts where should I attach a magnet plate? (I don't usually put my phone into any sort of protective cases.)

Thanks.

Replacing back plate drops waterproofness?

Hey guys, sorry if this has been questioned before.

My back cover/plate/glass thingy is shattered and I am willing to replace it (just for curiosity I don't care about the glass crack itself - I mostly want to replace the back cover because of my cam's lens peeled off).

Some dude of mine told me that if I do that I will lose the waterproofity.

Can someone confirm that?

Thanks!