Is 20 guage too thin for smooth firewall?

[scherp69]

So on the weekend I made a smooth firewall out of 16 guage sheet metal. I was going to weld it on top of the old one (most of it removed though), then I got thinking and now I'm wondering if I would be better off running a flange all the way around, using thinner sheet metal so it is flush with the flange and saving some time trying to smooth the edges. Right now it's just held in place with cleckos. I've done a search of the threads and found different guages of sheetmetal that have been used, but none of the threads found have mentioned running a flange at all. I ran a test flange on a spare piece of sheetmetal and found that 20 guage fits pretty flush. 18 is a tiny bit too thick, but would probably work with a little grinding.

Or...do you think I would be better off leaving if the way it is now. The more I look at it, the only places I would have to grind to make it fit a contour would be along the top and around the tranny tunnel. The other areas would blend in pretty good. What do you guys think???? Here's some pics of what I've done.