Modeling of trust sustainability and evolution among partners of a dynamic Virtual Organizations (VO) whose collaboration is already established, poses high challenge to such virtual co-working environment. Research in VOs has not established suitable modeling approaches for analyzing evolution and sustainability of rational trust and related assessment mechanisms for the collaboration which is already in progress. This is very necessary as it has now been proved that the base trust level acquired by VO partners during the VO formation is not static and cannot to remain constant over entire period of collaborative business execution. Thus proper modeling and analysis approaches for measuring the continuous changing of trustworthiness of organization need to be developed. This paper proposes approaches and mechanisms for modeling and assessment mechanism for supporting inter-organizational trust sustainability and evolution.