Made from 2 marine battery boxes, some 3/8" threaded rod, nuts/washers, tubing, and some hacked up bungee cords.
If you look at the pics it's pretty easy to tell how it goes together but please ask if you have questions.
It will hold a pretty good amount of stuff and it was less than $30 to build. rides fine with plenty of heel clearance (i wear a size 12). My next project is to make bags that mount independently on each side.
Yay for utility cycling!