If you are doing a 3kw to 4kw tracker, then GET THEM units quick that's cheap.
I would if I were in the US.
800lb base unit looks good, especially if you consider that my 2kw trackers are 450lbs with the PV panels on, the design is not my recommended design for trackers as the main loading is allways on the rotating point......but something to experiment with.
Normally the actuator and the actuator fixing points to the frame, need some serious consideration and are always a nuisance to get the design geometry correct, as these take the full loadings of the storm winds.
One of my trackers, cost me about $800 material costs, but excludes the PV panels.
So that 800lb lump, if it works right, looks real nice as a base unit to play with.