The duo said it was their preference to travel by sea and rail and avoid flying if possible.
“I had two pulmonary embolisms and the doctor said best not [fly] if you can avoid it and I’m very happy to avoid airports,” Imrie said.
Morgan added: “You see things in American trains that you would never see if you drove or if you flew.
“We’ve seen the wildest of animals – alligators and roadrunners, bears, orange pigs – and eagles.”
The pair will make their appearance at the Cheltenham Literature Festival on Friday 16 October.