I use 3 coats of Polyurethane on mine. The property owners where my hives are at like the natural look. Oh, and my boxes are "decorated" before the poly by my two little girls. They like to put flowers, bees and butterflies on them so they are more like home. It helps to individualize each hive also.
This is my second year using poly. The only problem I have had is with the bottom boards weathering quickly. First year of use and they look bad! I may paint them when I get them out of rotation this year.