Another option is to wear a canister-based breathing mask while welding, specifically designed to remove heavy metals and similar pollutants. If you have such a mask from painting vehicles, that's the one that will do the trick.
Because they're fairly large and cover a fair portion of your face, you'll never get your welding mask over the canisters so you can adapt and use them a different way as I have. The canisters clip on my belt and I clip them behind my back, then run a flexible plastic tube from my mouth to a fitting I machined which the canisters screw into. I call this a "back breather" because I'm breathing filtered air from behind my back through the canisters. The mouth end has a piece of a "snorkling snorkle" I hacksaws the mouthpiece off and glued the tubing in.
Of course if you don't have a canister breather apparatus to begin with, it's an expensive option to make one as compared to purchasing ordinary mild steel tubing that's not zinc coated.
Electrical conduit is not really a structural tube, it's designed to contain fires and burned wires and nothing more. It's bent easily with simple lever-based anvils and with the very thin wall they have little strength after getting a few dings, dings that are likely on a moving kart.
You'd probably be better off with mild steel tubing with a 1/16-1/8" wall to be honest.
BTW, any kind of welding produces noxious fumes that can kill you. Vaporized zinc just makes those fumes even more noxious.
