We consider applications of mobile wireless sensor actor networks (MWSAN) that require periodic readings and/or actions. In such a context, a single integrated sensor-actor can be used to monitor different regions of the target area if it is able to move from one region to another within some expected time limit. In this paper, we propose a mobility strategy that consists in making nodes follow a space-filling curve with good locality properties (i.e., regions close on the curve are also close on the area). This strategy has a number of advantages, such as higher possibility for merging readings when these latter present high spatial correlation (as in the examples listed above). We also propose that nodes use opportunistic contacts to reduce the delivery delay performed by the sensing module. Through a number of numerical analysis, we show that with a proper dimensioning of the system, we can achieve full area coverage and guarantee bounded delivery delays with a limited number of sensor-actor nodes.