sonofsand,
I saw this trailer on CL, are you from the Rochester area? I am closer to Syracuse but I often check out the Rochester CL section. That is of course where I saw this with these exact pictures.
My recommendation would be a Burley Nomad or Flatbed. The Flatbed may be better as you plan on modifying it yourself. Here is a link:
http://www.burley.com/products/flatbed.html