It's working now. The following slice of pie was causing a hick-up earlier; I needed to add another single quote to each side of the ResType and StatusCode parameters.

Non-working code:

AND (' + @OperParam + @Date_String + ' AND AL1.reservation_type IN('' + @ResType + '') AND AL1.status_code IN('' + @StatusCode + ''))'

and the Join I used looked like this...

=Join(Parameters!ResType.Value,"'',''")

Working code:

AND (' + @OperParam + @Date_String + ' AND AL1.reservation_type IN(''' + @ResType + ''') AND AL1.status_code IN(''' + @StatusCode + '''))'

and that join needed to be changed to this...

=Join(Parameters!ResType.Value,"','")