We regularly have to deal with garden sheds that have a steel channel on the bottom of the walls that sits on a concrete pad (non rebated pad). When it rains, water seeps under these channels into the shed and we are wanting to find an effective way of stopping this. I though that putting a piece of timber on the inside of the shed around the base and using an appropriate sealant could work - interested in your comments.
You should be able to use a neutral cure silicone such as Selleys 'Brick & Concrete Silicone':http://www.selleys.com.au/sealants/silicone/brick-concrete/ or Selleys 'Roof & Gutter Silicone':http://www.selleys.com.au/sealants/silicone/roof-gutter/. Whether you need to use a strip of timber or not I don't know. As long as the metal chanel and the concrete are clean and dry the sealant should be sufficient as long as it is applied to provide a good seal all along the gap between the ground and the base of the metal chanel.