Earliest, likely, record I can find is from the 1851 census:

Newland. Stowe Green.
Edward Gilbert Head 58 1793 Beer House Keeper and Lime Burner
Elizabeth Gilbert Wife 60 1791

This is the only record of a beer house or similar in the area so assume it's the Travellers rest.

I can find an Edward and Eliz Gilbert in 1841 census but he is listed as a farmer living in St Briavels. Could be the same. The location of the Travellers Rest is right on the parish boundary between Newland and St Briavels.