Anthony:
In the '50s, nearly all mobile homes were what we would today call "park models," because they were still of a size and weight that could be towed behind a car. If the trailer was large, it did take a powerful car, though: When M-G-M made The Long, Long Trailer with Lucille Ball and Desi Arnaz, a Lincoln had to be brought in every so often, because the Mercury used for the rest of the movie couldn't handle really bad hills while towing the New Moon seen in the film.
Starting in the late '50s, you began seeing mobile homes that required truck delivery. Within ten years, those became the standard, though people still continued to call them "trailers." That term applies only to models that can be towed with a car; if your car can tow half of a 32' X 80' Palm Harbor double-wide, I wanna see what the Hell you're driving.
Anyway, that A-B range would have been a nice, deluxe touch in one of the era's trailers, maybe even an upgrade feature.