Hi Maggie,
Obviously the place to look for his baptism record is in the parish records for Etchigham, but I have this one Etchingham marriage from the Sussex Marriage Index,
Etchingham, East Sussex, Date: 2 Apr 1782:
Thomas WENHAM, widr
Deborah NOAKES, (lic)
This is Joseph's marriage, does the extra information help?
Ticehurst, East Sussex, Date: 20 Jul 1772:
Joseph WENHAM, bach Etchingham
Frances CRUTTENDEN, sp otp (B)
Witness wit: Jn.WICKHAM; J.POLHILL
jane