To achieve a natural look and feel whilst protecting the wood, we recommend using Osmo WR Base Coat (4001) to help prevent mould and rot.
Once dry, use Osmo UV Protection Oil Extra which will nourish and protect the wood whilst slowing down the natural silvering / greying process caused by the suns UV rays. The oil dries to a durable, moisture repellent finish that is easy to maintain. Both the Osmo WR Base Coat (4001) and Clear UV protection Oil Extra 420 will darken the wood slightly giving a 'damp' like appearance. You can get an idea of how this will look by wiping the untreated wood with a damp cloth.
If you feel this is too dark, then you could have a look at the Osmo UV Protection Oil Natural 429 from the same range, this one has a minute amount of white pigment in to counter the darkening. To reduce / avoid the darkening that the Osmo WR Basecoat would create whilst preserving the door prior to oiling, use a suitable wax free wood preservative prior to applying the Osmo UV Protection Oil Extra.
Sample sachets of the Osmo oils are available and doing a test area is strongly recommended as the type, age and condition of the wood will influence the final finish. In other words, the same product applied to 5 pieces of different wood will likely give a different finish on each.