Because there are no commercially available leaf springs that would give as soft as suspension as I was looking for. The rocker arms allow me to get the wheel travel and rate I desired with an off the shelf spring-damper.
You can't take a 2 leaf pack and remove one? I'd be worried that a soft trailer suspension would sag too much and the trailer would roll left and right in turns.
Try boxing your trailing arms to add stiffness. Redoing the arms with thinner wall but larger diameter tubing plus boxing may be another option.
Are the 3/8" rod-ends going to be strong enough to handle cornering loads?
I have actually done that with leaf spring trick with my dad's gas trailer. That trailer is built off of the 40x48" harbor freight trailer and carries a 100 gallon gas tank (yeah fill ups on that are $$$). When the tank is full the trailer weighs 950-1000 pounds. The trailer uses 2 leaf slipper springs. As an experiment I pulled the second leaf out and well greased the slipper. The ride was significantly improved but still a little more firm than I'd like. My trailer won't ever be loaded that heavy (I hope). I have also heard that running monoleaf may speed up fatigue in the springs which worries me a little bit.
Eventually I will do something to improve the rigidity of the swingarms and I will probably lose the rod ends in favor bronze bushings before putting it on the road. In the meantime I'm going to be working on doing all the little tedious things like brackets for lights, fenders, deck mounts, cargo mounts, etc. I'll have plenty of time to think about exactly how I want to change things. For right now I just want to move on to something else to keep it moving.
Another one of my goals with this project was to get people talking. It certainly seems to be succeeding at that!