The cover should be three retirement-age, black-habited nuns riding in an open convertible. The convertible is large and yellow (a Mercedes-Benz-like car but not copied from any exact model). The time is mid-1960s.
The nun's cowls are black with a band of white framing the face—a standard look. Their hair doesn't show. The nun at the wheel is plump and wears round glasses. The nun beside her is thin and doesn't wear glasses. A small swath of red hair might show from under her cowl. The nun in back is medium-sized and wears black-rimmed glasses. The women are enjoying their ride, and on the car hangs this sign: Rome or Bust!
In the background might be countryside fields, or perhaps little towns—The nuns are Irish, but they are driving though France and Italy. The women and their car are more important than any background.
The basic look of the cover should be lively and cheerful. Probably lots of yellow. This is a humorous book, and these three nuns are the troublemakers for their bishop, who has been trying to cheat them out of their convent and land.