Arturo Almaguer, 44, must serve 30 years behind bars before he can apply for parole.
A jury convicted Almaguer on Monday of capital murder in the deaths of Evan Squires, 70, and his wife Wilda Squires, 65.
The couple was from Minnedosa, north of Brandon, and escaped each winter to the Magic Valley Trailer Park in Weslaco, Texas.
They were found shot to death in their mobile home, wearing their pyjamas, on the night of Nov. 13, 1988.
The case remained unsolved until 2011, when authorities said they matched feces left on the floor of the trailer with DNA from Almaguer, arrested in Michigan on an unrelated offence.
"We went 23 years with no hope," Wilda Squires's son, Bill Jury, said Tuesday after Almaguer's sentencing hearing.
"With DNA you can run, but you can't hide."
The son sat through some of the trial and said the prosecution argued his mother and stepfather were killed in a burglary gone bad.
The couple, married for two-and-a-half years, were both regulars at the trailer park when they met and fell in love. Evan Squires taught painting classes there, and Wilda Squires taught English to children at a school just over the border in Mexico.
They were kind, trusting people who even had a habit of not locking their door. Jury explained that the couple wanted their older neighbours to be able to come in and use their phone if they had medical emergencies.
It was alleged that Almaguer believed no one was in the home that night, because the Squires had parked their vehicle in a neighbour's driveway to make room for some renovation work.
Court heard Almaguer piled a box of silverware, a portable radio and other belongings by the trailer door, then went to use the bathroom. When the Squires woke up and confronted the intruder, he shot the couple and defecated on the floor.
DNA testing was still relatively new at the time, but Jury said an investigating officer decided a sample of the feces should be collected and stored. Experts were later able to collect enough skin and blood cells to create a DNA profile.
Jury said he's relieved the criminal case is over, although Almaguer has already filed an appeal.
Note to readers: This is a corrected story. An earlier version said Almaguer could not apply for parole for 15 years