They way people in southern Thailand do is soaking them in drying oil (linseed, tung) then wipe them off and let them dry. This is enough to keep bamboo/rattan work for 10-20 years. After the oil dried, you may also wax them to give an extra protection.
But there the problem i the rattan getting too moist... where I am the concern is that it'll dry out, crack, and fall apart...