However is any of this documented anywhere? I can not get this to work though I can connect happily via the command line using psql
Additionally, not strictly an issues with RPostgreSQL, the sslrootcert option mentioned in the answer linked to above only takes the name of the certificate file, i.e. not the path to the file. The expected location of certificate files is documented here: http://www.postgresql.org/docs/current/static/libpq-ssl.html