I think copper is too soft to use for the electrodes, and I'm not an expert in metallurgy, but I don't think it would be safe to use, either.
I'm glad you didn't wipe yourself out :-). That would be research as a self-limiting function, wouldn't it :-)? Us live Researchers are a high-ticket commodity, you know..
Hulda Clark had her zappees (of which I am one) wrap their copper pipe electrodes in wet cloth or paper towelling so their hands wouldn't be touching the copper metal directly.
I figure that's enough for me. I wouldn't want to soak in it :-). Although it might be worth checking into if someone had Arthritis, since many of with Arthritis seem to benefit by wearing copper bracelets, etc.
The mfg using the copper tub is not driving electricity through it, they are just using it as a reflector. I think their name (which is posted elsewhere on this board) is Hymbas. Maybe they have an FAQ and maybe it mentions this..