In the Corvette, I use a keyed disconnect switch for security purposes, and since the glove box is right next to the battery box, the switch is hidden inside there and the red plastic key, which is attached to a removable keychain on my regular keys, has to be inserted and turned before I can start the car. I also have my electric fuel pump wired to an on/off toggle switch which is hidden under the ashtray.
On my Firebird, I have one of those battery post-mounted switches which you unscrew the knob to disconnect the battery and those work well too. For ease of installation and simple disconnection, they're probably the best. And yes, you mount them on the negative post.
I've always assumed that this is because electrons actually travel from negative to positive. Our system of labelling is actually backwards, from an engineering point of view.
