The Leroy trailers are amazing-looking (but expensive), and you can build a trailer that's just as useful (or better, if you have custom requirements) for under $500 using a red trailer kit from Northern Tool or Harbor Freight and bolting on a full-width, waterproof, ABS pickup truck box. Four tires will also fit, stacked two-by-two and sitting side-by-side. I used one of these for years, towing it all over the country behind my Miata for autocrosses, and the only maintenance was repacking the wheel bearings once a year. When I got home, I just stood it up against the wall in front of my car until the next event. Google "autocross trailer" and you'll find a bunch of examples like this one:
http://www.wizco.net/MX5/Mods/autocross_trailer.htm.