Hou flew home after six months. Zhang continued through Turkey, Iran and India.
He barely speaks any foreign language and relies on body language and Google Translate.
"Toilet" is the most important English word, he says. He learned it from a French hitchhiker.
"I always meet warmhearted people who help," he says.
A Chinese couple in their 30s invited him to stay a week in their home in Sofia, Bulgaria. They drove him around and sent him off with rice and vegetables.
He gave them money. They secretly slipped it back into his pocket.
"They said it was like an elderly relative visited, and they were happy to see it as a family reunion," Zhang says.
Indeed, RVing - a longtime retirement-life staple in the West - is catching on among China's elderly.
"China's RV industry is developing rapidly," Zhang says.
"I notice more Chinese driving RVs to Europe. I hope more Chinese will enjoy this lifestyle."
The Chinese mainland had about 21,000 registered RVs by the end of 2014.
The number of campsites increased from nearly 40 in 2010 to about 500 in 2015, the Chinese Association of Automotive Manufacturers reports. It predicts 10,000 in the next five years.
