I finished the first draft version of the parts of the chassis.
Here are some photos showing the technique that I usually use to build the cross bars.
I checked, while I was building the prototype, that it is very important to build parts thoroughly, making straight folds and I found this:
I scored the fold in the back and I used tweezers to make the folds straight.
The model of the trailer is becoming complex: only this part of the frame has 52 parts.
More to come.
Best, Nando