Hi Phil, I have looked at Wissett PRs for you today at the RO as best as I could, some of it is very feint. After 1813, the Wissett PRs have been transcribed and indexed and bound into a book so this was obviously far easier to search.
I could not find a birth or baptism for your Joseph Dawson but did find some information on the Mayhews (most of it post 1813). You may know this already, but I will list what I have found in case it is of some use to you.
All information relates to Wissett
Children of Robert Mayhew and Elizabeth (late Stocks):
George, baptised 4/3/1786
Mary, born 19/7/1787, privately baptised 22/7/1787, received into church 30/12/1787
Children of Nathaniel Mayhew and Hannah (late Balls):
John, baptised 26/6/1786
David, born 6/10/1787, baptised 7/10/1787
Children of John and Anne Dawson (late Cropton):
Rebecca, born 6/9/1789, bapt 7/9/1789
Charles, bapt 17/2/1793 (father listed as a pauper)
Children of Robert and Mary Mayhew (farmer):
Thomas Edgar baptised 2/10/1814
Mary, born 26/3/1818, baptised 13/4/1818
Children of Robert and Mary Mayhew (farmer):
William - no date but between 1813-1815
Charles, baptised 10/7/1815
Children of James and Hannah Mayhew (farmer):
Sarah, born 30/3/1826, bap 13/4/1826
William Spalding, baptised 27/2/1827
Thomas Spalding, baptised 16/5/1828
Mary Maria, baptised 12/5/1829
Fanny Spalding, baptised 7/5/1830
Burials
Grace Dawson (very feint), buried 20/4/1777
Elizabeth Mayhew of Halesworth, 1/3/1818 age 2
Charles Mayhew of Woodbridge, 10/1/1824 age 10
Edwin Mayhew of Wissett, 31/10/1824 age 5
Martha Mayhew, 30/3/1825 age 8
William Spalding Mayhew, 12/4/1827, age 6 weeks
Thomas Spalding Mayhew, 14/7/1828 age 2 months
Fanny spalding Mayhew, 9/5/1830 age 1 day
I hope some of this is useful, shame I couldn't answer your original query re: Joseph Dawson.
Regards
Anne