The "Gospel Wagon" was one of the "Papal plots" deployed in 1913 by the Catholic Extension Society in order to roam the Protestant strongholds in southern Texas in search of converts. Although the so-called "Motor Chapel" was said to get good mileage, it has nothing whatever to do with the fact the the Texas we enjoy today has an overwhelmingly high Catholic majority - this is primarily do to unenforced immigration laws in the Southwest.
The image posted above is a much faster Protestant version that appeared about a decade later.
Facts about American car ownership in the 1920s can be read here...
