For Waterproof installations, our EPDM rubber gasket kits will ease your worries. The are designed to precisely fit our Titan Post Anchors (4x4 and 6x6) and use a compression cylinder that fits in the cavity under the base of the anchor. You get a high pressure seal precisely around each screw that penetrates the substrate.
They can also be used, if you wish, on concrete surfaces where there are wet winter conditions with freeze and thaw cycles. They help prevent concrete from cracking over time.