Just for the fun of it, I placed a 30# box of kitty litter all the way forward on my BOB and a bathroom scale under the trailer's "drops." The amount of weight on the rear bicycle axel would be about 16 lbs. or less. If I moved the box all the way back on the trailer, the weight decreased to about 12 lbs. And these weights were probably on the high side because of the downward angle. The scale is lower than the rear axel of my bike, so lifting the trailer shifts a bit of the weight more to the trailer's rear wheel.

I only mention this, because it illustrates how much "gentler" a trailer can be on rear wheels. A two wheeled trailer could actually place "negative" weight on a bike's rear axel (not a good idea due to stability, though). Of course, I understand that bumps tend to hammer the rear axel some, but probably less than added weight via other means. Just thought you might be interested.