[Justin Stiltner]

I can lend my personal experience here,
I built a treb very similar to what you have there, I used only one 2x4 for the arm, no extra bracing at the center and had no problems using 300lb of counterweight. For my pivot rod I used a 2" piece of steel pipe that I had laying around, my thoughts about yours is that it will flex quite a bit, especially if you start putting a lot of weight in your box. Also, as others have said, you've got bracing on things that do not really need it, such as the braces from the base to the top of the pivot support, those are good, but the others triangulating them aren't needed. Mine actually looked like yours, but take out the 4x4 post going up for the pivot. Looks good though! Just watch that arm when you (so apparently the bad word filter decided that another word for load that started with a c is bad, so PULL THE ARM BACK) , that pin is dangerous! Oh and mine was 15 feet tall with the arm pointing up. All of my dimensions were true also, as in my 2x4 was actually 2" by 4" I bought them at a local small saw mill, about the same cost as normal lowes or Home depot lumber, but the guys picked out some really good ones for me when they heard what I was doing with them.