FTCA
Helping folks into and out of trailers is a garden-variety fucntion not susceptible to policy analysis, and therefore not subject to the discretionary conduct exception to the FTCA.
http://www.ca5.uscourts.gov/opinions/pub/14/14-31303-CV0.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.