Not suprising you cant find them really, in the 1841 and 1851 census (maybe 1861 as well cant remember offhand) it was not required for an enumerator to record people not living in houses. Generally, you are lucky if you find anyone.
Now Bob Dawson Ive always found to be an extremely helpful and amicable fellow, and I would suggest you contact him direct with regard to info on this family, and/or info on his book.
Here is how you can contact him directly
http://www.robertdawson.co.uk/contact.htmlWith regard to Moses Boswell, I found a few bits myself which might prove useful. Most of this came directly from the IGI online
http://www.familysearch.orgMoses Boswell b.cir 1815 d.1855 Etwall Derbys
married Trinity/Trenit/Traynet/Traynette (think it might also be Fraynet!!) Hasring or Herring or Hearn or Heron m.06.11.1826 Duffield, Derbys
Now I found they had at least two children:
Clara c.08.03.1835 Alfreton Derbys
Merner c.16.06.1844 Maxstoke Wrks
Then A* Moses Boswell *ie I dont know if its the same guy
had three children by a Mary which may or not be Trinity or Esther or someone else entirely.
Emma c.24.12.1838 Breadsall Dby
Gentilia c.25.12.1841 Breadsall Dby
John c.01.03.1846 Bradby Dby
Then Moses Boswell and Esther had:
Solena c.03.05.1822 Edibngale Stf
Henry c.20.08.1826 Sutton On The Hill Dby
Aaron c.18.04.1830 Rand Lincs
Elijahnesus c.31.12.1831 Horkstow Lincs
Eliza c.24.05.1841 Malpas Cheshire
Letitia c.06.05.1844 Leigh Stf.
There may be more hidden on the IGI I havent seen/found.
Trinity Traynet etc Hearn/Herring etc is Trenit d/o Miller Heron (aka Young) and his wife Winnifruita Boswell, daughter of Shadrack Boswell. According to the Heron Pedigree deposited with the JGLS by the Revd George Hall.
Miller Young appears on the 1851 census and reputedly was born circa 1791 in Yorkshire. He was a widower.