would like to incorporate built in bench for storage. Any advice on keeping it water tight please share.

An exotic wood like Ipe will be your best bet for low maintenance; all you have to do is oil it once a year to preserve the color. I've seen lots of Ipe benches like you describe, and they always look great:

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Depending on the exact shade of brown/tan you're trying to match, you might also consider Tigerwood or Cumaru. Both are just as low-maintenance as Ipe, but they cost less and offer a little more color variation.

Be aware any wood will need maintenance to keep the original color. Left alone, most woods turn gray naturally. The maintenance generally consists of using/adding finishes designed to stop UV ray damage from the sun as necessary.