I can't remember the thread, but someone was talking about trying to find some corrugated polystyrene like GoLite uses.

I found some at TAP Plastics. 2'x4' sheet for $5.50. The corrugations run in the 2' direction. They had some 4x8 sheets, but I don't remember the price.

I also found some tubes, epoxy and wound filament, light and stiff. Don't know how it compares to carbon fiber, but I picked up a couple of lengths of it. $3 for 2' or 3' length. They had varying diameters too.

Could you just use some expired political election signage? That stuff is "coroplast"--a corrugated plastic. I've used it to stiffen the bags I use on my bike.
--jd

I'm sure its the same stuff. And, its the season! ;-)

Problem is, do you trust a politician behind your back for that long?