Hi,
On Free Reg there are 21 baptisms for Thomas Jones between 1808 and 1812 in Caernarvonshire - of these 3 involve Jane as the mothers first name. I think you can probably discount two of them - parents David/Jane and Robert/Jane.
As their son Evan was born 1833, using a naming pattern, the most likely option is a baptism for Thomas on 15 July 1812 at St Peter and Vinicula, Mellteyrn, Caernarvonshire - parents Evan Jones and Jane.
Locationwise - Sarn Mellteyrn is about 3 to 4 miles south of Tudweiliog.
Any thoughts?
Alan