HiddenField to post to external website AND submit data to sql database with Masterpage

Hello.  I need to send some parameters to an external website using the <asp:HiddenField /> controls and also at the same time, submit data to a sql server database.  The part for submitting the data to the database is working, but I need to try to get the parameters from the hiddenfields to also be passed through.  I thought all I had to do is create the hidden fields and in the code behind, set the values from the textboxes that the user would fill out. 
My source code is below:


<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
   <!--Other controls above the hiddenfields.-->
<!--external class created called "wtd" to strip off the Masterpage renaming of controls in view state-->
    <wtd:HiddenField  ID="UPAY_SITE_ID" runat="server" />
    <wt ...