What is the best way to send data between dynamic widgets in GWT

Question

I'm building GWT page with a dynamic widgets withing other dynamaic widgets. Here is the example of what I have:

1. Course widget that is holding course name, course start time, and a list of Module widgets
2. Module widget has module name, module type, a List of Document widgets, and a List of Audio widgets
3. Document and Audio widget has simple text fields in them (name, url, time, notes, etc).

I'm using MVP pattern in my application. So, my question is, how do I communicate all this data from Document and Audio widgets to a Course widget and then save it to the database by sending DTO through RPC.

My Course object has List of Modules, Module has List of Audio's and Documents.