I believe that exp pedals should give digital output signals , while wah's should be analogue.
I don't think this is gonna work , unless there's a specific digitech wah pedal that can do it , and specialy since they don't mention "how" in the manual.
Anyway , since trying is for free , you should give it a shot... Here are your two possible choices :
1) Guitar to Wah I/P - Wah O/P to Exp pedal I/P - RP100 O/P to amp
2) Guitar to RP100 I/P - RP100 O/P to amp - Wah O/P to Exp Pedal I/P . (you should connect anything to the wah's I/P , in order to connect it's circuit)