One "Excess Cargo Carrier" from Harbor Freight, $40 on sale
Hardware: About $25
One 8"x6" pressure-treaded 5/4" deck board
One 3/4"x36" steel pipe
One 1/2"x 12" steel pipe
One 3/4" pipe flange
One 1/2" pipe flange
To attach the pipe flanges to the deck board:
Eight 1/4"x2" hex head bolts
Eight 1/4" stop nuts
Eight 1/4" fender washers
To attach the deck board to the cargo carrier:
Four 1/4"x1.5" bolts
Four 1/4"stop nuts
Four 1/4" washers
Two red bungee cords
One old bike inner tube
Step 1: Cut the board
Drill two holes at each end of the board, and two in the center of the board. Drill corresponding holes on either end of the cargo carrier, and through the 2" hitch bar.
Step 2: Mark and drill the holes for the pipe flange.
Then, drill holes on the underside of the board so that the fender washers and the stop nuts are recessed. This will allow the board to lie flat on the bed of the cargo carrier. Bolt the flanges to the board using four 1/4" bolts.
Step 3: Install the vertical supports
Mine uses two:
One is a 36" x 3/4" pipe with a right angle fitting on the top. This one holds the handlebars. I happened to have an unused bike carrier from Rhode Gear, so I reused one of the rubber holding straps; you could easily use a bungee cord instead.
The other is a 12"x1/2" pipe, which will hold the back wheel.
To protect the bike from dings and dents, I covered the pipes with rubber cut from an old inner tube. A 1.25" inner tube covers the 1/2" tube nicely; the 3/4" tube didn't fit, so I just wrapped the pipe with the inner tube and secured it with a cable tie.
Step 4: Completed Bike Carrier
I mounted the vertical pipes twice. The first time, with the bike pointing to the left, the drive train (the chain and gears) were on the same side as the pipes, which made them rub together. That seemed like a bad idea. So I moved the flanges so that the tall one was on the right instead of the left. Of course, that would have been easier if both of the pipes were 3/4" pipes.