Trocar assembly devices are disclosed that include an improved elastomeric seal member to maintain sealing engagement during off-centering or radial motion of instruments extending therethrough. The seal members include an inner section and an outer section. The inner section has an opening formed therein to permit an elongate instrument to pass therethrough in sealing engagement therewith. In accordance with certain embodiments, a corrugated portion is formed in the outer section. In accordance with certain embodiments an annular floating ring separates the inner section from the outer section.