Did you see the one where a guy names ChrisF made one out of a square post? and it uses pop bottles? Its quite sleek. Either way, I was suggesting the "guts" of it to be RGGS and then you can build a nice surround using cedar to hide the trough/pop bottles. Its somethign I want to do as well but haven't found the time. You can also use those plastic windowboxes and have that sit over the water trough and then build a nice cedar surround if you want more soil depth and stuff.
RGGS is fabulous. Its the only way I can garden.
I'll try and find a link for you. We have a group on facebook too - join us!