Rosarito is a resort community. Around March 15th (spring break) the town starts getting busy. After Easter, it quiets down just a little until schools break for the summer. High season is throughout the summer until after Labor Day. Three-day weekends are always the busiest. The city of Rosarito hosts several special events each year, so check with the local tourism office for more specific information.
There are several terrific condo complexes and housing developments in the Rosarito area. One condo development -- La Paloma, for example, offers some of their condos on a daily, weekly or monthly basis.