I used penetrating oil (Penofin brand) to protect them. Can I use something else for longer protection?. Also, should I prep the wood, wash or sand or both?
For your area, a penetrating oil is probably the best item. You will protect the wood but will not have a film build which will eventually fail and peel. What you probably do not care for is the frequency of re-application. My experience suggest that after several applications the in-between time grows and you will find you should get a year or 18 months between coats.