If you decide to go the cheap route, here is one of the manufacturers of the black corrugated tubes (with smooth inside pipe). http://www.ads-pipe.com/en/product.asp?productID=177 There is one other manufacturer that I know of, but I can't find the web site.

I went to their web site and got the local rep number and called to see who the distributers were in Chicago. They come in 20' lengths, but the distributer I went to cut it and sold me a 10' section. Cost about $80. The end caps are around $35, but I picked up a design for an end-cap from the guys in CRAW using outdoor ply.

On the plus side, these are cheap, hold quite a bit if you get the 12" diameter and they are light and easy to secure to the trailer. On the downside, they are kinda ugly.

PM me if you want to see a picture.