That doesn't sound too bad. I'd probably go with 1/4" stainless round bar stock. When i ran bags a few years ago, I screwed a plywood backer inside the bag rather than add the bag supports. Didn't work too well, leaked around the screw shanks. But the gal I sold the bags to seemed to like them that way. She had them on her bike at a rally later that summer (mounted backwards).  

If I was to try bags again, I think I'd try the Marauder spec hardbags, don't need the support bars. Since my bike doesn't have fender rails, I could hard mount them to the fender sides...
-WD