Privacy Fence: Is this minimalist design efficient?
For 30 years, assuming concrete, I'd go with un-boxed metal u-channel posts.   I'd put bevels on the rails. A 45 degree bevel on the top. It should slant away from the pickets  to shed water and dirt away from the pickets. And a 15 degree drip-edge bevel on the bottom to keep the water from running back towards the pickets. I'd get full inch rough sawn air-dried pickets from a saw mill, not the 9/16" pickets from big boxes, though there is something to be said for more rails and thin pickets.

And since price/labor is a function of the number of pieces, I'd use (2) 2x6's for the rails instead of (3+) 2x4's.