I've always put three to four coats of Danish oil on my arrows and then attached the fletching with hide glue or Tite Bond 3, oh, I also wrap the front and back of the fletching with sinew or B-50. Never had any problems with the fletch delaminating from the shaft with either hide glue or Tite Bond. I don't know if the results would be the same if I sealed the shaft with Polyurethane.