There are a couple of candidates for Benjamin's parents as the Parish Records have two births around the approximate date.
1) Benjamin Trigg b 1787 Mitcheldean to Richard Trigg and Elizabeth Jenkins (married 1778 Weston-under-Penyard)

2) Benjamin Trigg b 1791 Mitcheldean to Benjamin Trigg and Priscilla Welsh (married 1779 Newland)

For what it's worth I have the line you are investigating under 1) above, but you may see from my previous post in this thread - I was looking at this branch a long time ago and cannot at the moment see any other relevant indicators.

Regards
-Colin