Just a quick reply (I haven't been able to look at all the new projects posted today -- computer was freaking out for a little while, but it's behaving again whew!). I have been contemplating using something like you used for the base of a hat. Do they work for big Gainsborough hats out of curiousity, or best for smaller hats like that?
Also, the trim you used around the crown? You know the green dress/leine outfit I wore to classes during CLW? I had a little reticule with the same trim in green. Ha!
Hrm...I think it would be possible to use plastic needlework canvas for a Gainsborough. You'd definitely have to wire the brim, and possibly at intervals (so multiple concentric circles of wire, if that makes sense.) The needlework canvas is heavier than buckram, so that extra wiring would help stabilize it. I think it also depends on the weight of your fashion fabric. If you use something lightweight like silk, it might not be necessary to do the extra wiring...but something heavier like velvet could make it too floppy. This is all speculation of course! It's inexpensive and readily available, so I definitely think it'd be worth some experimentation. :)