There are several types of cutoff switches to choose from. Weigh them all out for your specific need. Mine is a four-way Perko marine switch with the choices of bat#1, bat#2, both or all off. One switch in one place anywhere it's easy to get to. Some install their switch on the neg line, although I have no idea why. Mine is on the positive side just like in my boats which came from the factory that way.
Oh, and good luck with the Optima bats. I'm sure you paid dearly for them. What total amp hours will they deliver?
2013 Silverado 2500 HD Duramax/Allison Tuned
Aviator Wright Flyer #1919
"First In, Last Out". 11B4Y
DAV, MOPH, VFW, 5/7 Cav,1/8 Cav Assoc.
11th ABN Pathfinder Co. N7MIP