Try a couple of heat shrinks in the centre first , nothing to loose , oxy acet if you have it , and a damp rag.
I did wonder that, but was worried it might distort/pull in stuff that isnt currently distorted. You dont think thats a risk here?
I dont have oxy, but can use the welder puller thing. Done that before for shrinking, works well.

Had oil canning on the deck panel on my charger after id welded in a replacement. Did a spiral of welds and it pulled it flat and tight. I have tig too. Just no oxy 
