To me it looks like a gusset plate needs to be made with the same profile about 100mm and fully welded in.
As Mega suggests remove the rubber and glass, sand it back to bare metal and tack in the gusset then fully weld .
OR,,, you could weld as is and quench the weld with a very wet rag as you weld small bits at a time.
This may save a lot of time and have you back on the road earlier.
To me this would not hinder door seal or the way it closes