Ms Gowing's body has never been fully recovered, although remains were found at two rural locations near her home in Flintshire, North Wales, and near Chester.
Clive Sharp, 47, of no fixed address, pleaded guilty to her murder at Mold Crown Court last month.
Mr Justice Griffith Williams ordered that he serve a minimum 37 years behind bars before he can be considered for parole.
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The children - who are two of three triplets - were found not breathing at a property in Bridgend, Wales.