I believe that 87MH's response up top was the correct one: 23 US gallons.
Just remember that means only slightly over 19 Imperial gallons to us Canadians, or 87 litres.
Good grief! I just noticed that you are just "down the road" from where my trailer lives! We are just a bit south of Westport. I think that makes your AS TTs the closest one to Henri, my TT.