Lisa and Mick Patterson were about to start unpacking the vehicle when their son spotted a man walking away.
When they confronted him he admitted he had secretly hitched a lift through French and British customs.
They believe he hid under the £35000 (R608000) motorhome in a campsite in Caen, northern France, for three days before balancing on the axle as they made their way home, through Calais.
The youth, who claimed to be a minor, was arrested and is now being dealt with by Home Office officials.
Lisa Patterson, 50, of Essex, said: “My son said there was a black man walking down the street. We live in the sticks and no one walks down here. I ran out and called him over. He was a really nice person from the English he spoke.”
She added: “I asked him where he hid and he went back under and showed me. He was balancing across the back axle.
“We asked him how long he had been under there and he held up his fingers and said, “Four”. We said, “Four hours?” and he said, “No, days.”
The stowaway, who is believed to be 17, emerged from under their motorhome when the family returned earlier this month.
The drive from Caen to Calais is three-and-a-half hours, while the time spent on the ferry and in both ports would have been about two-and-a-half hours. After reaching Dover, the Pattersons spent more than two hours driving non-stop to their home.
A Home Office spokesman said: “A male, who claimed to be from Sudan, was arrested for immigration offences.” - Daily Mail