Anyone (in 10 mins) can create their own $30 very strong bicycle trailer out of an ordinary hand truck.
Bruce Thomson in New Zealand explains in a slide show a demo of many he's made & used in many years. Also gives 'surprise tips' on safety - attaching & carrying loads. These trailers take tiny space to store (vertical). Note: With years of hard work, wheel bearings fail. Watch for wobbly wheels, replace/re-sleeve them. With huge weights, the tubeless wheels sheared their bolts going over deep pothole or steps, so don't put more than about 250kg while towing. Walking the bike 'safer. Can take big 8'x4' wallboard though, if you extend with a 4"x2". & rear crossbar. P.S. See other vids:''No need for bicycle trailer - vertical load the carrier' and "World's cheapest 'Vertical recliner' bicycle", "Double glaze doityourself for 1500 dollars". May 2013: Created 1M wide swap-in axle for stability. SEPT 2013 Have just bought some (used) skateboard wheels, with a view to making a super-compact, telescopic-collapsible , strong trailer small enough to carry all the time on the bike. If/when it's done, I'll create a video and mention it on this video too.