Niko:
I believe Chris has a heater that has three (3) double pole feeders. He said the panel is outside, so 'in site' is out of the play. I don't know of any handle tie for 3x2 pole cbs. Also, A six pole disconnect is another animal I have not seen.
An acceptable means may be a lockable panel cover, or a cb lock for the main. A debate with the local AHJ may be a way to work out a solution>
