Thanks for the feedback guys. I agree, it would be stronger with a frame member connecting the top of the steering pivot tube with the top of the shock mount. That would take all cantilevered members out of the main frame. I will add something like what you have mocked up if it turns out to be an issue. The main frame tube and the steering pivot tube are both Cro-Moly tubing. The steering pivot tube is inserted all the way through the main frame tube and welded at the top and bottom. Again, I agree there is a huge bending force at the intersection of those two frame members, I just think the frame members are up to the task. As you mentioned, adding that extra frame member would limit what you could put on the frame. I'd like the basic trailer to be easy to customize for people to haul what ever they need. Obviously, I would not reccomend hauling a huge amount of weight, staying under 100 pounds would be best.
The shock actually works very well. On the first trailer I made I used a mountain bike shock. Like using the MTB wheel, I figured that the trailer was light enough to utilize the MTB shock. I was wrong on both.. The small motorcycle shock is very stiff by itself, I cannot compress it at all with my hands. However, the mechanical advantage that the wheel has over the shock is about 7 to 1 the way I have it mounted. I weigh 250 pounds, I can sit on the rear end of the action packer container and almost bottom out the shock if I bounce up and down a little. On the road and trail it soaks up the bumps amazingly well. I will try and get a video made and posted up very soon so you can see it in action.
I have found that I need to lengthen the trailer a couple inches. When you put the ActionPacker tub on the trailer and mount it behind a Dual Sport bike with a stockish rear license plate/blinker holder there is not enough room to allow the trailer to pivot up while riding a wheelie or perhaps going up a short steep hill. So the next one will be a little longer.
I've loaned out the trailer pictured to the guys at ProCycle to get some feedback. So far they are loving it! They have used it to haul a motorcycle frame across town to get sandblasted. They have used it to deliver a few oversize gas tanks. One of the guys took it home for the weekend and plans to use it to go grocery shopping and run other errands. They even added an LED tail light on the back and wired it into one of their bikes. I asked them to use the crap out of it and not be careful with it. If it breaks, I learn something! It appears I'm going to have a hard time getting it back though, they really like the trailer.....