I guess you need to define what you mean by long term, to me that means being layed up link for a hip replacement or setting back a gun for someone in the family to get when you are gone. I had an experance similar to eldeguelloand hes right if you used cosmoline and it sits for 3 years it would take white gas and a good brush to get it off I useR.I.G or RIG as we call it, to presever the guns that I am not presently shooting.
For normal use on the guns I shoot every month I use Sheath, or as its called since they changed the name Barricade , its made by Birchwood Casey. Lee