I use the same but suspect any oil would do. No skimping on this one I'm afraid, if you get drenched put in the extra effort and strip the rifle, dry off any excess water, let it dry out and get it oiled up before putting it away.
One little tip I have for you is to always carry a black bin bag with you. They scrunch up to nothing and if you find yourself in a heavy downpoor just put it over your rifle