Hi rolls rolls,
Why do you want to implement your own class inherited from Telerik.Cms.Web.CmsPageBase? Doing this, you cannot change the default functionality of Sitefinity, since you cannot replace the existing Telerik.Cms.Web.CmsPageBase with such a class.
Probably, you want to override Telerik.Cms.Web.InternalPage, which also inherits from Telerik.Cms.Web.CmsPageBase? InternalPage class is the code-behind of the page which is responsible for live pages output (~/Sitefinity/cmsentrypoint.aspx):
|<%@ Page Inherits="Telerik.Cms.Web.InternalPage" MasterPageFile="~/Sitefinity/Dummy.master" %>
Please let us know if you need further information.
the Telerik team