When I built my island, i have it on the trex boards to get it off the concrete patio and with the "grooves" facing down, there are a few small channels for water to flow under slightly and I then covered the entire floor of the inside of the island also in the trex with grooves in the same direction. I have no metal or item storage on the concrete directly. I think based on the feedback above use the Hydroban type of coating since I am in the holding pattern currently due to the holidays and occasional rain.
