Trowern was a new name to me too. Working backwards is bit of a nightmare as all sorts of different spellings such as: Trenen, Trourn, Truem, Trouern, Trewern to name but a few!
Sarah's mother Caroline Mary S. Trowern was the daughter of William Trowern and Jane Ley who married Topsham, Devon 29/6/1851 - William was a Ropemaker, son of John, Ropemaker.
Williams birthplace on census varies between Cornwall and Devon. However, although I can't find his baptism there the 1841 census shows he was born in Cornwall.
1841 Census - Phillack, Cornwall
John Trouern 55 Rope M. J. (Rope Maker Journeyman) - Y born in County
Peter Trouern 15 Shoe m. Not born in County
Elizabeth Trouern 15 Not born in County
William Trouern 12 Born in County
(ages were rounded down on 1841 census hence 2 15 year olds.
John Trowern married Honor Thomas 9/3/1806 Antony, Cornwall but can find no baptisms of any children born to them between 1806 and 1817 and then there is:
Charlotte bc.1818 Devonport (per a tree on Ancestry)
Caroline b.29/12/1820, bp.5/2/1820, bp.5/2/1821 Morrice St. Westleyan, Devonport, Devon
Peter Thomas b.14/11/1822, bp.3/12/1823 ditto
Elizabeth b.1/2/1825, bp.6/6/1825 ditto
William bc.1828-1829 Cornwall
John Trorvern (yes, another version) was buried at Phillack, Cornwall on 1/8/1846, his wife Honor on 29/9/1865 Phillack aged 80 (she is not with family in 1841 and can't find her on any census before she died.)
Since John was a Journeyman the family clearly moved around but no idea where they were between 1806 and 1817 as I'm sure there must have been children born in this time frame.
Annette