See that horizontal groove? That will allow any water that accumulates underneath the base or in the tubing frame to drain away. If the stanchion you buy does not have such a groove you might want to cut one in yourself.
Freezing water aka ICE can exert a lot of force if allowed to collect in tight places. Best to prevent that anyway you can.
Life Calk for the bedding of the bolts. You could also other bedding materials like butyl tape if you want.