Best Friends (1975)

Mature, stable Jesse, his nutty and impulsive longtime best friend Pat, Jesse's caring fiancé Kathy, and Pat's fragile gal pal Jo Ella all decide to embark on a cross country road trip in a Winnebago prior to facing the challenges of encroaching adulthood. Relationships between everyone become increasingly strained as things take a turn for the worse and the journey turns into a severely bum trip for everyone involved.