It depends on how the Trust wants to focus its funds. Similar to how a VC fund might focus on enterprise software or B2C. For a reference of Self-Storage REITs, this is a good start(1).
Different markets are definitely hotter than others. Houston, Miami, Austin, Los Angeles are some of the more lucrative markets, but even small markets have strong players. Self-storage is fairly democratic in the markets served. I've visited facilities in rural town that are wildly successful for the owners, as well as small facilities outside of Manhattan Beach.