3S2P does triple the voltage; however, i you look at the max input for your charge controller, if that is not exceeded, it will step it down to the 12 volt charging/float voltage Automatically. In my case, it’s 100 volts, so I could not hook all six panels up. In a cold environment, voltage out in the panels goes up, so my 18 VMP may actually put out more than 20, so that would exceed the VMP.
I think you meant all six in parallel, not all six in series. For parallel, a fuse for each panel would work with a properly rated breaker that can take constant on and off, like a 150 VDC midnitesolar breaker. If your charge controller is 100 volts VOC, than you’d not want to hook more than 4 panels to it if these panels put out around 18 volts.
The MPPT charge controller I have can take a max of 720 watts 12 volt or 1440 watts 24 volts. Doesn’t matter if its a 20 volt input at 36 amps, or 80 volt input at 9 amps, the charge controller will still put out 720 watts. It may be a little more efficient at 20 volts, than 80 volts, but not a lot.