I see a lot of search results where people use the 1/8" with no problem and did not find anything saying it did not actually work.
those tanks do have the top and bottom brace though.
in my case, one side can be full of water to the top, and the other side only halfway. But considering max pressure is at the bottom, I see no reason why 1/8" cannot hold 6" or even 12" deep water pressure.
I was considering this option, as 16" x 20" is like $5 and another $3 for the cutter.
I see some people double it up. it will still cost less than getting from a glass shop. I think it's the labor that is expensive, the glass probably costs minimal.