The PON project studies container loading when objects are nonorthogonal, but their shape is represented in terms of polyhedra.
Links:
[1] http://www.iiia.csic.es/en/individual/vicenc-torra
[2] http://www.iiia.csic.es/en/individual/isaac-cano
[3] http://www.iiia.csic.es/~vtorra/projecte.pon/