Gas gives a nice flat weld whereas TIG tends to have more bulk but heat flows through aluminium at such a rate that, in my experience at least, there’s nothing to choose between the state of the metal whether you use gas or TIG. I started on gas and now use TIG exclusively.
You still have a large area of material very close to meting point as you go and it normalizes in the same way when you take the heat off. If there’s any doubt you can rub some soap on it and heat until the soap turns black to anneal the metal. By far the most important factor with wheeling welded seams is getting the metal back to the original thickness before you begin. If someone can tell me how to post pics on here I’ll pop a few on.