Gas - of course! "A Perfect Dedome?" (https://budgetlightforum.com/t/-/17374) 
. The cut/heat method works of course, it's just more prone to error for me. I could view vinh's video a 100 times and I'm still unsure exactly how's it's done, or how to be sure to get consistent results. The gas method is very consistent. Dale is bringing up some good pts about possibly less tint shift using the cut/heat method, some may say less output loss as well. Since we lack accurate data on this, it's a tough call but hopeful sign, just don't have data or a technical explanation/theory on why.