Be aware that for small, low copy number genes the sensitivity of the process may be limitted. Thus you should consider using some kind of amplification - TSA usually works fine - in case you do not se any signals with the probe.

Furthermore. I am using the procedure described by Subrot myself and i works quite good. However, the DIG labelling does reduce the effeciency of the PCR reaction, so don' t be supprised if you get low quantities of probes following labelling and purification. With some probes i often get as low as 300 ng following the reaction.