Robert Hume and his wife Catherine planned to be at the caravan in Aberlady, East Lothian, on the night of the blaze but had to return to their permanent home in Whitburn, West Lothian, at short notice.
The day after they left, their caravan, and another mobile home based at Aberlady Station Caravan Park, was deliberately set alight.
Mr Hume, who is registered disabled and occasionally has to use a wheelchair, was gifted the caravan by his father-in-law so he and Mrs Hume, 56, could be closer to him after his wife died.
They had planned to stay in the caravan all last week, but were called away to attend appointments near their permanent home.
But in the early hours of Thursday morning, their mobile home was one of two left gutted in a deliberate fireraising attack.
Several others also suffered thousands of pounds worth of damage in the incident.
Mr Hume, 57, said the couple had been left distraught – but admitted it could have been much worse. He said: “There’s nothing left of the caravan. I was in shock when I saw it, I couldn’t even speak.
“My whole body just felt like it had gone to rubber – my wife hasn’t slept since.
“If we hadn’t had to leave to go back through to Whitburn, my wife and I would have been in the caravan when it was set on fire.”
The £150,000, five-person caravan was bought by Mrs Hume’s father John Colquhoun, 83, from North Berwick, so they could be closer to him after he was widowed.
The couple are now waiting to find out if insurers will cover the purchase of a new caravan.
Robert said: “I would be a bit wary about going back to the caravan park, but I would like to buy a new one.”
The owner of the Haddington Road caravan park, Andrew Dyer, said four people had been staying on the site at the time, one of whom raised the alarm.
He said: “I’m so disheartened that this has happened in a small village like this.
“We’ve never had anything like this happen to us, it’s such a quiet community.
“It will have an affect on the business, because we’re at the end of the season as it is – it could have an impact on next season.”
Lothian and Borders Fire and Rescue Service sent two units to the site after being called at around 1am last Thursday.
Police are now appealing for anyone with information about the fire-raising incident to come forward.
A force spokesman said: “Fortunately neither of the caravans were occupied at the time or this could have been a far more serious incident.
“Nevertheless, these fires resulted in several thousand pounds worth of damage and we are carrying out local enquiries to identify those responsible.
“Anyone who was in or around the caravan site in the early hours of Thursday morning and remembers seeing anything suspicious is asked to contact police immediately.”
Anyone with any information can contact Lothian and Borders Police on 0131 311 3131 or Crimestoppers on 0800 555 111.