Best thing I have found to keep the cedar looking good is raw, not boiled, linseed oil with around 7% beeswax in it. I also have an aversion to screws and nails as they can provide opportunities for water ingress into the wood. With modern adhesives, such as Titebond III, and good clamping whilst the adhesive dries / cures, I have found nails and screws no longer necessary.
But as I am sure you know, or are finding out, beekeepers disagree on almost everything - so listen to them all and make up your own mind.
Can we have a thread on the best coatings or preservatives for matchsticks? It is not so much their cost as the hassle of having to go round all the hives checking and replacing the failing ones, so as to ensure good ventilation through the winter...