Hey berntd,
I am wondering why your use of TIG seems to be the priority factor to obtain thick/thin fillet welds. I do agree with the other guys on their suggestions with TIG, but the entire process you are trying to accomplish can be so much more effectively done with MIG, especially when you have many holes to do. When I weld the classic car floorpans(.020-.025) to the frame metal(.187-.230), I use .030 ER70S-6 @ 175A and when the puddle forms on the frame and fills the hole(.125dia.), there is a sweet button of weld that completely seals the pan metal and frame together without any elongation of the pan hole. It is fast, hot, and works so well. Just curious....Denny