I built an HF trailer with a cargo box as well. I did make a few mods to it though, I both narrowed it up (about 4 inches if I recall correctly) to just fit the box between the fenders and shortened the frame to be just a little longer than the box. It's just a little wider than my side boxes. I considered moving the axle inside the springs, but did not like the effect it had on the angle of the tongue on the hitch as it made the tongue ride nose high. That condition can make a trailer want to wag around. I did add a deck to mine with some 3/8" plywood (I think). The ply adds not much weight, does help keep it square and I think help keep the frame from twisting. I did lengthen the tongue about 12 inches. I do not have a full swivel hitch, but I do use a long neck ball. If the bike ever took a nap it might bend the tongue, but otherwise I could drag the pegs if I wanted to.
It came in about 150 pounds, but we never load it very heavy, mostly bulky, but light items... camp chairs, the tent, a small bag of clothes.... etc. Fully loaded I doubt it goes much over 225 pounds. After it was finished, I made several test runs with bags of quik-crete in the box to test handling, etc. On my last test I had 5 bags in it (80 pounds each ~400 pounds). It handled well with that load, but I could REALLY tell it was behind me. With our normal camping load, I can barely tell it's back there, but it does cost me about 2 MPG at highway speeds.
Definately repack the bearings though. And you won't need full pressure in the tires. Lower pressures will help with the trailer bouncing.
We've towed it about 8K miles and never had an issue with the smaller tires, I do carry a spare as well.
As for chains or no chains..... I do run chains to the bike. If the hitch ever came off the ball, I would rather the bike go down and know the trailer was still attached. While a rogue trailer shootiing off and hitting another vehicle would be bad enough, I don't think I'd ever forgive myself if it hit or killed a person walking along the road.