However, the inside of the feeder pillar in Plate 3 (R150, ~10-15 years old, just a few feet above a river) was very wet. There was condensation running down the sides of the enclosure and the backboard was clearly damp, with some mould growing on it. The base was unsealed and, most likely because of the high water-table in that location, there was significant water ingress.
Apart from looking unsightly, the marine grade plywood backboard had still maintained its integrity and felt solid after well over a decade in those conditions. Also, as expected, there were no signs of corrosion on the pillar body either.