Welding 316 Stainless 1.5 mm onto 2 mm for the Solar Panel Frame

We were making a frame for the solar panel, some of the 30 by 30 box section 316 stainless, I brought from the UK it had a 2mm wall thickness, which is really the thinnest I can weld with arc welding, we needed more stainless steel, and all we could get in Gibraltar, had 1.5mm wall thickness, which caused problems with welding it.
TIG welding would have done a much better job.