Mobile systems monitoring is an application area for Mobile Wireless Sensor Networks (MWSN), which introduces some specific challenges. Delay/Disruption architecture tackles some of these issues, such as delay and connectivity disruptions, and thus has already been used in this context. However, WSN nodes have severe limitations, concerning storage and processing capabilities. This performance problem has not been investigated as it deserves and this is the purpose of this paper. We propose the FREAK scheme which aims at reducing the computation while performance remains high. This scheme relies on the mean frequency of past encounter with the base station. Transmissions are driven by this metric. The FREAK solution is keen because we assume that future can be predicted from the past events. We also analyse the acknowledgements effects on performance. Our proposition is evaluated through simulations based on real traces. FREAK is compared to several replication and quota-based mainstream DTN solutions and achieves quite better performance in realistic scenarios.