I'm interested in welding some stainless tanks/containers using 0.048" (#18) sheet. I've seen folks do this on YouTube, without back purge. I tried a couple of test pieces, and the back is not good, 'sugared' I believe is the term, exactly like the videos show on WelderSkills. I watched Roy's video using aluminum foil to contain the purge gas, but as the tank is sealed up, that becomes difficult. 

What do people do, or are the final welds always crappy on the inside?