Mar-K :
2 coats of semigloss POR-15
followed by
2 coats of Behr semigloss black
I visited Mar-K a few days ago. Their wood finish test is still ongoing. This is a current photo of the test boards with the POR/Behr black finish that was begun back in about 2005 or 2006. it has been outdoors in the Oklahoma sun and weather 24/7 since then and still is in good condition. I know the OP inquired about oil finish, but if long term durability is the goal, this system is worth considering.
Mark
