Abstract: An add-on seat assembly is provided for temporary attachment to the rear of a vehicle. Such seat assembly includes a hitch bar, one end of which has, intimately associated therewith, a structure and arrangement for releasable attachment to a trailer hitch which is intimately associated with the rear of a vehicle. The hitch bar includes a securement structure extending across the opposed other end thereof. The seat assembly includes a pair of arms that are demountably and rotatably attached to a respective one opposed end of the securement structure. The seat assembly also includes a pair of seat units, each including a seat bottom that is foldably secured to a seat back, the bottom of the seat bottom including a structure for demountably and rotatably attaching the seat unit to a respective one of the pair of arms.