Yep Doug, if you scroll down, you'll see I was the first one to respond to Donny's how-to. (As 'Reefed_One', with an underscore.)
I hope I was diplomatic enough. He really did do an excellent job, with the sole exception of pipe selection. However, that can't be overlooked--IT'S LIKE AN EXTRA BOAT!--as 230+ pounds of deadweight could be a HUGE safety compromise on a light-duty trailer: stressing the springs and tires, affecting handling, balance, high-speed stability, and tongue weight, increasing braking distance, and possibly increasing the chance of a jack-knife incident. (Not to mention gas mileage, ease of maneuvering by hand when un-hitched, and SINKING IN THE SAND... AMHIK.)
I'm going to be in home-improvement "urr, urr" mode next week, so I'll check on prices for THIN-wall PVC duct pipe, end caps, etc.
As far as ready-made, it's like Bizzaro-land! I have a 1998 Murray's catalog, and the "Toy Box" is $250... now in '05-'06 they carry something similar from my buddies at Performance Cats called the "Sport Locker", and it's $800!! WTH?? Is it carbon fiber with a solar-powered dehumidifier built-in? Should a mere tube cost more than the sails they protect? Does this make sense? Where's my PVC primer and glue... lol.