Custom Fields in Mail Merge

Hi, I created a custom Module with different custom fields that I have related it to the Potentials Module. When trying to create a template for the Potentials module in Mail Merge, I can't find the custom fields that I have created. I even added a Product to the Potential, and also can't add any fields from the Product in the template. Is there something I am missing? Is there a way to connect any Custom Module or Field directly to the Potentials Module and then use that information in Mail Merge?

Thanks