Get a sound in the subtractor you like, then move the frequency on the filter quite near to the bottom, then move the attack (a) to roughly the middle on the filter envolope below it. that should do the trick!
i found in using reason the best way to get that wob sound is to use one of the patches on subtractor or send the lfo to the filter, you can then can change the speed of it by increasing/decreasing the rate. the best lfo waveform i find is the triangle
good luck