Two brothers have each been jailed for 30 months for conning elderly people into paying for ineffective insulation to be fitted under their mobile homes.
Nathan King, 38, of Tewkesbury, Gloucestershire and John King, 34, from Barnacle near Coventry, had earlier admitted conspiracy to defraud.
They said they could make homes warmer but the bubble pack-style insulation installed was not fit for purpose.
Residents were overcharged with many paying for other unnecessary work.
Nathan King was the sole director of Guardian Park Homes Ltd and was imprisoned for 30 months and disqualified from acting as a company director for five years.
John King played a leading role in the business and was also jailed for 30 months.
Leon Williams, 29, from Coventry worked as their foreman and received a 10 month prison sentence suspended for two years. He was also ordered to do 200 hours of unpaid community work.
The men were sentenced at Newcastle Crown Court after previously pleading guilty to a charge of conspiracy to defraud on the first day of their trial at Teesside Crown Court.Image copyright North Yorks Trading Standards Image caption The bubble pack-style reflective insulation was stapled beneath mobile homes
In mitigation the court heard some "legitimate trading" had taken place and all the defendants had expressed remorse.
But His Honour Judge Ashurst described the Kings as "brazen, greedy and unscrupulous men" who had behaved in an "outrageous way".
"The public would not understand if a fraud of this type was not met with an immediate custodial sentence," he said.
Police had been called to a park home at Skipton in North Yorkshire in March 2015 by the site manager.
He was concerned an 82-year-old resident who lived alone and was having work done on her property was being misled by workmen who were going to charge her £7,000.
The workers - including Leon Williams - were arrested. Trading standards officers from North Yorkshire County Council launched an investigation and seized Leon Williams' phone.
It contained numerous postcodes referencing mobile home parks where trading standards officers found further victims who had been defrauded by Guardian Park Homes Ltd.Image caption Ruth Andrews, Head of Investigations and Safeguarding at North Yorkshire County Council's Trading Standards Dept.
"Nathan King and John King had been doing the cold calls to park home properties," said Ruth Andrews, the head of investigations and safeguarding at North Yorkshire Trading Standards.
"When they identified a victim that was going to have the work done they would text the postcode to Leon and the team."
The gang had worked on park homes in numerous other areas including Bath, Northamptonshire, Lincolnshire, Lancashire, Cumbria and Gloucestershire - which was where the company was based.
'Danger of collapse'
Park homes look like bungalows but are raised off the ground on metal supports.
Barrie - a pensioner who lives on Teesside - was told by Guardian Park Homes that his property could collapse because its metal supports were rusting.
But a surveyor appointed by trading standards officers later found the anti-rust paint they applied at extra cost was unnecessary and the insulation he had also paid for was useless.
"My first feeling was of anger that they could have done this to me," said Barrie.Image copyright North Yorks Trading Standards Image caption The insulation was often so poorly sealed it would have proved ineffective anyway
"I couldn't get underneath that floor myself to see what needed to be done or to check it when it had been done, so I trusted them completely.
"It made me feel frightened to make any more judgements of people, frightened to trust people again to do any more work."
Twenty-seven victims were included in the court case with losses totalling more than £100,000. They will be getting their money back after trading standards officers discovered a similar amount of money in frozen bank accounts belonging to the Kings.
The Kings found no shortage of people willing to pay to make their properties warmer because there is limited insulation, even in newer park homes.
Extra insulation can be added beneath them or to their external walls or roofs. But Ann Barradine, director of the not-for-profit organisation, Community Warmth, which vets and monitors contractors doing such work, warns that if air vents are blocked, a home's wooden frame can rot and collapse.
"There are some excellent companies out there that will do it properly, she said. "It is absolutely abysmal that somebody could go into an elderly person's home and rip them off."
You can hear more on this story on You & Yours on Eyes On Events Radio 4 from 12:15pm on Monday 1st May 2017.