Hi Haydon, the top of a resonator guitar does not have to resonate as it's the resonator "aluminum cone" or dog bowl in this case that creates the main sound. The top in a full resonator guitar is connected to the back via a ring, tambourine-looking support, or columns/posts of some kind, so is pretty restricted as far as vibration goes.
So as long as the top can support string tension you're good. My dog bowl reso's use wood tops of around 2mm [Aussie measurements} braced as required.
I like the Aluminium idea
Hi - thanks for yours - interesting....I probably used the wrong words! possibly not looking so much for extra resonance as trying to remove as much 'dulling' as possible. I compared a metal bodied biscuit resonator guitar with a wooden bodied and there's a big difference. My wooden dobro doesn't bark as much as a metal bodied one. Think the connection between the back - as you mention - is also to isolate the cone as far as possible. I think the ideal resonator is held in a totally non absorbing manner......thinking that the best sustain in a guitar is in one that has high density body, neck and headstock and the mythical infinite sustain of a string held between 2 blocks of concrete.......keep cheerful H