Greg,
Thats about the same wall thickness I used and had no trouble getting it welded. My tube was 1.25" ID, 1.5" OD. There was no engineering involved in choosing the tube size. That size is just what I had laying around the shop. I would guess that 1" ID would work just as well. Looking at the tubing used on the FLYGAS website, the tubing that crosses from one side to the other appears to be somewhere around 1".
Bear in mind that I'm a just a shade tree mechanic and was pleasantly surprised that the thing actually worked. Hope you have good luck with yours.
Bill.
