Books

L. Fatibene, M. Francaviglia,
Natural and gauge natural formalism for classical field theories. A geometric perspective including spinors and gauge theories. 
Kluwer Academic Publishers, Dordrecht, 2003. xxii+365 pp. ISBN: 1-4020-1703-0

L.Fatibene,
Relativistic Theories, Gravitational theories, and General Relativity
in progress (forever)