As for the oil treatment, I painted a new board fence, common red oak boards. Red oak is not the most durable wood in the weather but it lives in very similar conditions as a trailer deck. It wasn't until about 20 years that I had to replace any of them.
If it's not the rain, it's the sun drying out pt. that will be it's eventual ruin and all pt is not treated equally but it's still probably the 2nd choice if you can't get white oak. That's excluding the exotic rain forest woods that is just stupid expensive for the average occasional use non "over the road" user.