At the Animal House (a really nice LFS in Corvallis, OR) they have a few plywood tanks in the 200-400 range that have been there longer than I've been going there (21 years).
This is the only pic I could find, you can see a bit of the frame.
my mom worked their about 20 years ago, and she said she remembers those same tanks I visited it a few years ago, but i do not remember seeing them - i wish i had thoughAnyway, just backing up what dan said