Any finish that creates a coating that will seal the wood will seal in moisture. The wood will rot from the inside, it has been said.
Wood needs to breath.
Only apply poly to completely dry timbers, if ever...
If you want smooth timbers then don't work with hand hew stuff, work with planed stuff, or re-work hand hew by the method mentioned above.
Most timbers are just oiled, for color and preserving....
Just my opinions....
