There are better battery disconnects, but you may get by with an inexpensive knob model -- see "swan battery disconnect." The recommended safe practice is to install it on the negative/black/- terminal, and the instructions may likely mention that. The oversized nature of the shutoff brings it potentially closer to other metallic items, including during a crash. Since the negative terminal is already grounded, that's not a problem, whereas the positive side will start sparking as soon as it contacts anything metallic. It's easy to check for parasitic draws using a $10 Harbor Freight multimeter (volt meter), you can Google that or watch a YouTube video.
