Don't use TRUE tung oil; use something such as Formbey's tung oil finish or I use Watco Danish oil on my cameras http://www.tystintypes.com These are not true tung oils, they are varnishes. Make sure to wait about 5 days after your last coat before doing anything else. Stay away from Polyurethane.

Oh yea, and wax does work great as a final step.