I have some painful experiences here. :cry:
Stay away from the lightweight dual rail "dirtbike" trailer. Years ago, I lost a hub (cracked around the stud holes) and flipped one of these dragging it down the freeway upside down with two Commandos lashed on. I was lucky as one had a fiberglass tank that could have ended in a big fire. Damage to the bikes was surprisingly limited.
Your choice of a tow rig and how far you expect to take it would be my main determining factors in selecting a trailer. A lightweight open "landscaper" trailer with a drop gate works well if you are using a 4-cylinder truck or car to tow it. A minimum of 13 inch wheels if you are traveling anything other than short distances at speed. Smaller wheels spin the bearings faster. A drop gate makes one person loading and unloading much easier. Downside is the bike is subject to weather, wind, and objects dropped from passing vehicles. Never cover the bike with a tarp while towing this way. The flapping tarp will destroy your paint.
If you have a full size truck or SUV, an enclosed 6X10 with side door and drop gate is great. It gives protection from the weather and if you are traveling overnight, provides a lockable "garage" to keep prying eyes and fingers away. Also, if a tiedown should fail, the bike won't fall off the trailer at speed. A bonus is it provides additional weatherproof storage at home.
We have been taking my buddy's enclosed 6X12 to Daytona the last few years and it seems ideal. Tandem axle with electric brakes, V-nose for better aerodynamics, and plenty of room for two bikes, gear, spares, and the swapmeet treasures we bring back. The tandem axle gives peace of mind in the rare occurence of a blow-out.
Think about this when you tow your Norton, it's probably a $6-15K value that goes beyond money in investment in labor and pride. Are you willing to see that destroyed because you wanted to save money on a trailer? It's a scary sight to look in your review mirror and see your bikes bouncing off the freeway by the safety chains. :shock:
If you can't afford to buy a good trailer, rent one. :wink: