For this test I split the barrel object into smaller more manageable pieces.
That way it's easier to place the seams. I merged the pieces again after
activating the SubDiv Modifiers which makes the SubDivs editable.
The UV Unwrapping algorithms produced distorted UV islands.
And Pinning UVs was not an option because many of the seams
are in very dense areas and selecting points is a nightmare.
And in the UV editor there is no Loop Select.
So I unwrapped manually with the UV Mapper tool, section by section.
Flat for everything except the cylindrical shaped areas. Making note of the scale
of the mapper is important so map the largest section first and write down the scale.
This is because if you use the Center Projection command everything goes to zero and 1/1/1 scale.
The unwrapping algorithms offer the convenience of one click operation but they may not
behave as you expect because they may not like the way the seams are made.
This will be the final map...probably.