Lynn continues to deny the murder but conceded he destroyed the couple’s remains and much of the campsite’s evidence.
Justice Croucher described the killing as “violent, brutal and horrific” when he handed down the sentence on Friday.
Burning the remains was an aggravating feature and showed Lynn’s moral culpability was high, Justice Croucher said.
“This was just a terrible thing to do, hence my conclusion this is a very grave murder,” he said.
Justice Croucher noted the “profoundly moving” statements from Clay’s loved ones, who remembered her as a loving grandmother.
The judge also broke down in tears as he acknowledged Hill’s family, including his wife Robyn.
While they were not considered victims in the eyes of the law due to acquittal, Justice Croucher said it was clear they were also in pain.
“As one person to another, as a matter of common human decency, I should acknowledge their plight, their agony, their suffering – and I do,” the judge said.
He also took into account that Lynn led police to the remains and apologised for his “despicable” actions after the murder.
The judge said that “tempered” the aggravating post-offence conduct, although only modestly.