End members (202, 204) dimensioned for securement to an associated flexible wall (206) of a rail spring assembly (200) can include an end member body formed from a polymeric material and can have a longitudinal axis (AX). The end member body can include an end wall (232) that extends transverse to the longitudinal axis. An outer side wall (234) can extend longitudinally from along the end wall. An outer peripheral wall (264) can extend from along the outer side wall and can be dimensioned to abuttingly engage the associated flexible wall. A plurality of support walls (272) can extend between and operatively interconnect the outer side wall and the outer peripheral wall and thereby buttress at least the outer peripheral wall against loads applied by the associated flexible wall. Gas spring assemblies including one or more of such end members and suspension systems for rail vehicles including one or more of such gas spring assemblies are also included.