Have there been any studies looking at RF exposure over long time periods?

Yes.  There have been studies of people exposed to RF energy over a long period of time.  The epidemiological studies have not shown adverse health effects at exposure levels at or below the FCC standard.  

The World Health Organization (WHO) maintains a comprehensive searchable database of research in the effects of electromagnetic fields on biological systems, available at http://www.who.int/peh-emf/en/.