We have finished one rail 8650mm long and 5.80m at 9″ high and 2.85 at 12″ high.
Massive beam, which is calculated to carry 5.5t at a required strength of 1/6th of the yield strength of the material.
The whole trailer is calculated at 6t maximum capacity at off road standards.

We will do the second rail tomorrow.

I also received another bunch of Visduinos today from China and am doing a few more compatibility tests.
The Visduinos appear to be better than some of the Arduino clones I got from an Australian seller (most likely also from China).