You may remember be talking about research carried out by Bath
University and the Caravan Club of the UK -- well, after 20 years of
research(!), something has finally been published on the web.

http://towingstabilitystudies.co.uk/index.htm

There's not a whole lot there, but that reflects the fact that
stability is pretty simple: have at least 7% of the trailer weight on
the hitch (up to the towcar's limit), and concentrate mass low down
around the axle.