Since I did a considerable amount of my 4th year away I feel qualified to answer.
Some schools DO have housing available (but they require you to pay for it): anything at the Texas Medical Center and UCSF-Fresno are two that come to mind. Others may provide you with local students or others in the community who will rent you a room. This is what I did at most of my rotations. Particularly in college towns, there are lots of elderly people who may or may not have some affiliation with the university (ie, retired professors) who rent rooms to visiting students. The rooms are furnished and you usually have some kitchen access.
When you inquire about doing a rotation ask if the program has information on available rentals in the area. If they do not provide that, check the classifieds for rooms to rent, although this is probably somewhat more risky than something the university provides and has obstentsibly had students use before (whether on or off campus). During 4th year lots of students do visiting rotations, especially during the fall, so you may also be able to find students who are willing to rent out their room or apartment for the month while they are gone.
Best of luck!
