“If I didn’t make it, no one else in the world would,” he told the Sun on Sunday.
“Nobody else knows how to and it’s my best yet. I wanted to do something special to honour King Charles.”
The design of the 3250kg coach is inspired by Rolls-Royce limousines and is due to be completed this year.
Mr Frecklington is hoping King Charles, 75, and Queen Camilla, 77, will pay it a visit on their current tour Down Under.
Mr Frecklington’s prostate and bowel cancer has now spread to his lungs, which means his work has “slowed down a bit” because of both the illness and fortnightly chemotherapy sessions.
He said he corresponds with King Charles about his progress and had gone to great lengths at his own expense to turn it into a “time capsule”.