Alan writes in to say that he is a a great great great grandson of Thomas and Zilpah Goodman, and gives details of the later generations who also lived at Rickmansworth. He agrees with my suggestion that there is a possible connection with the Sloper family in Wiltshire.
Sloper is an unusual surname - commonest in an around Wiltshire, and I decided to see I could find any possible Sloper relatives who had moved to Hertfordshire. I found a Rev. Charles Sloper, who was the minister at the Independent Church at Hitchin between 1817 and 1825, when he died "of a broken heart" having lost many of the congregation!