yes self tapping screws, but with some internal spline lock washers. You don't want these to vibrate loose, especially while tooling down the hi-way. Just make sure that the mounts are sturdy too. If it were me I would make them so they could be removed and placed in the TV. Speakers are not as rugged as you think. A couple of good jarring bumps and the voice coils could get damaged and when that happens the coil could short out frying the output transistor on your stereo, which means you would lose one side of your stereo at the very least!
You might get lucky and have it just get stuck so as to not go in or out and not make anymore sound. I would advise a permanent installation...that is...unless it's just some mounts for the speakers.
Tom