I gauged the draw bar height by attaching a towbar to the chassis of the trailer. It will be the same towbar I'll put on my van. It's a bit of trial an error as you can see, it's a bit custom at the front and worked around the spare wheels. I found running the drawbar parallel to the floor of the tub worked best. That said, I can remove the chassis whenever I need to as it is mounted using factory body mount rubbers..... Its not a permanent attachment.
Feel free to post progress pics of your trailer