I just had an idea but keep in mind i'm not a body man and never used it...
When i was getting ready to do my gas door my uncle also recommended using a flanging tool, but he also recommended using automotive body adhesive like is used in the newer body repair, i don't know anything about it but think its probably a 2 part epoxy?
Maybe there is just too muck area to assemble and squeeze into place tho not sure. Then how to squeeze it all into place? Cleco's perhaps?
http://search.eastwood.com/search?p=...d&w=Cleco&rk=3
Ether way i like the flanging idea and agree i think it will be helpful to keep it ridged.