If you have room in the battery box and are willing to maintain the terminals and workings of a disconnect switch (that high acid environment is an enemy), a cheap disconnect switch is the answer. If you wish to have no problems and understand that your battery "lease" is not trivial in $$$, you'll want to use a better switch, mount it outside the battery box, and use the (+) phase of your battery wiring.
Blue Sea makes a good marine one that withstands the weather. I chose to use Cole-Hersee
M750 as it is the best one I could find. CH does make a single pole disconnect, as does Blue Sea, and other marine brands. These can be mounted to the side of the battery box.