In Industrial IoT (IIoT) environments and especially for applications relying on Mobile Nodes (MNs), ensuring communication security is a critical requirement, in order to prevent attacks that aim to obtain sensitive data or compromise MNs. In this paper, we focus on the security of IIoT systems based on the 6TiSCH architecture defined by the IETF, in the presence of node mobility. We propose a method for provisioning key material to MNs, enabling the enforcement of a trade-off between security and overhead. Specifically, we consider three security settings, characterized by different security levels and communication/storage overhead. For each setting, we evaluate the impact on performance through simulation. Finally, we provide a set of guidelines to help network operators in the selection of the setting to use