Here's a couple of pics of my latest flatbed.

-Bought a typical used kiddy trailer with probably less than 5 miles on it for $25 on craigslist.
-removed all canvas and repositioned a few braces
-installed a 3/8 piece of plywood that I had laying around, painted it brown with some left over house paint.
-I bought a new Burley elastomer hitch and installed it on my touring trailer, removed the old one and it installed right on this trailer.
-total investment, maybe $35.
-weight: 18 pounds without plastic tub.