For the purpose of this chapter, the word "trailer" is defined to mean any vehicle or structure which is suitable for living, sleeping or office purposes and is mounted upon wheels, or is so designed or equipped that wheels or other devices for moving the same can be affixed thereto, and which can thus be transported either by its own power or by external power or effort. This definition shall not include any vehicle operated upon fixed rails. (1976 Code § 96.010)