I'm pretty sure some type of apartment building is far more efficient than an RV park. A trailer or RV park is still sprawl, even if each unit occupies less space than traditional detached homes. Sprawl is bad - it creates dead dormitory towns were people have to drive somewhere else for almost everything.
The problem is that even with balconies and maisonettes, people tend to find such apartments boxy, cramped and unattractive. But they certainly make it easier to provide good public transport, district heating, broadband etc. as well as services like stores and cinemas to a large number of people at once, and in parts of Asia, these types of apartments are the norm.
