VANETs currently represent one of the most prominent solutions that aim to reduce the number of road accident victims and congestion problems while improving the quality of driving. VANETs form a very dynamic open network in which vehicles exchange information and warnings about road situations and other traffic information through several routing protocols, without any intermediate control. However, the absence of a central control makes such a network vulnerable to several types of attack, not only from the outside but also, and mostly, from the interior. This makes their detection by classical security techniques more difficult and requires the development of new techniques to control the information circulating in the network. In this context, a proposed routing protocol called TDMA-aware Routing Protocol for Multi hop communication in Vehicular networks, is vulnerable to security threats, such as Black Hole and Gray Hole attacks, as well as MAC attacks such as Denial of Service (DoS), which lead to a considerable deterioration in the network's performance in terms of packet delivery ratio, end-to-end delays, channel access rate, etc. To mitigate the effect of those attacks, we propose a trust-based model in which each node will establish a trust relationship with its neighbors based on their behaviors during the channel access and packet forwarding process. The simulation results show a significant decrease in the effect of attacks on the performance of the TRPM protocol.