Two "good Samaritans" went to the aid of the couple - believed to be in their 70s - as six car-loads of young people attacked the campervan about 1.15am on Saturday.
The couple, from Mosgiel, were asleep inside.
Several windows were broken, panels dented and doors buckled and twisted.
A can and a bottle were thrown into the van, where the frightened woman was in her nightgown covered in glass while the man tried to drive the van away.
Constable Greg Park, of North Dunedin, called the attack "despicable [and] cowardly".
"We are pursuing this investigation with vigour.
"If the offenders don't come forward, we will be throwing the book at them."
David McLaren and his partner Norma Hart, of East Otago, were spending the weekend in a house truck at the domain, north of Dunedin, and said they were awoken by shouting about 1.15am on Saturday.
They saw the Mosgiel couple's van and the man trying to drive away from about 18 young men and women, who were kicking the sides and windows of the van and throwing bottles at it.
At least one person was jumping on the roof while another swung off the passenger door.
Mr McLaren went to help as Ms Hart rang the police.
All the young people left.
Mr McLaren and Ms Hart comforted the couple until the police arrived about 20 minutes later.
The couple were escorted to Dunedin by police and made their own way to Mosgiel.
They did not want to be identified or speak to the Otago Daily Times on Saturday but the man said the woman was "in a state of terrible shock".
"It's shocking that something like this can happen," Mr McLaren told the ODT.
The elderly couple told them the youths had surrounded their van and begun to shake and rock it when it was parked at one end of the domain, about 200m from the house truck.
The shaking woke the couple.
"The man told us he tried to back the van out to get away from them and accidently nicked one of the group's cars and that was what set them off," Mr McLaren said.
He said a carload of young people he suspected had been involved in the attack returned to the domain before police arrived.
Several people got out and began walking around, searching the ground.
When he asked what they were doing, they said they were looking for a lost dog.
"I started to have a look around, too, and saw a cellphone. That's what they were looking for, I'm sure. Who looks for a dog at 1.30 in the morning?"
He passed the cellphone and the registration numbers of two cars to police.
Const Park said the elderly couple were "freaked" by the attack, although they were not physically injured.
"Terrorising elderly people like that is just not on."
Police had already spoken to a group of young people from Dunedin whose vehicle matched the description of one seen at the domain.
They denied being involved.
"Very strong evidence" had also been collected at the scene, including fingerprints.
Calls made on the cellphone would be analysed and its owner identified.
Police were "closing in" on the group, Const Park said, advising them to turn themselves in.
