Yeah, bugsoup has got an excellent idea! When I welded up my trim holes I burned through the first one really badly. My friend told me about the backing idea, and it worked beutifully. I used an old bronze bushing, that we cut and flatened into the right shape. Just take your time and get the backing plate as flush as possible to the back of the panel. Good luck and remember that you can only make good welds when you are relaxed and not frusterated, so take your time
Cheers,
Dave