Hi Charlie,
I haven't been on the forums in a while but while browsing I saw that you were thinking of upgrading your trailer hitch...
I saw a neat idea for a trailer hitch (that you might be interested in) a few days ago. I may adopt this method for my trailer(s).
Heres a couple of photos of it and a link to trailer & hitch...
Made from a steel tube and a swivel caster wheel.
LINK:http://www.instructables.com/id/SURF...ILER/?ALLSTEPS
As you can see it has all the movement a trailer hitch needs - Up - Down - Left - Right - plus it pitches (due to the swivel caster) allowing the bike/trailer to tilt when cornering.
I'll keep an eye on your build for any updates
Regards
Tom