I have some log benches that sit outside in the weather all the time. I try to keep them looking in good shape and apply some exterior spar varnish from time to time.
This does a good job, but I have found that it is best to apply this in very thin coats. If I apply it too thick, I will get little bubbles that surface and make the finish look and feel rough.
When I use a good, clean brush and make one pass with a thin layer it works a lot better. I wait until it is completely dry and apply another thin layer to give a smooth, glossy finish.