To avoid over-engineered for this specific case, you can just make "MSFT|AAPL|ETC"and string.Split('|')value. string.Join("|", values)for storage.
If you are faced with a situation where you need an object graph that is really complex, you can do :
<profile defaultProvider="AspNetSqlProfileProvider">
<properties>
<add name="FavoriteURLs"
type="System.Collection.Specialized.StringCollection"
serializeAs="Xml" />
</properties>
</profile>
, , "type", XML.