High quality primer/paint on the outside and dinitrol sprayed inside would be my choice. If you don't want to spend on the dinitrol, used gear oil, thinned with a bit of diesel, is ok for the inside. Old engine oil isnt good for you, or the environment, and also contains water and acids that may attack metal.
Some don't like polybushes, I do, never had a problem with them, and my friends drove a polybushed series from London to CapeTown, no bush issues at all. I would go for a premium brand rather than the cheapest you can find.