Dump file property field will not open

I have seen this question posted elsewhere but I can't seem to what needs to be done.

First, I'm not a developer, but I have a pretty good sense on how to use SOAPUI to send requests and get responses to test web services.  I'm trying to execute an eBay web service the returns a file.

As you can see from the screenshot, I'm sending the request and getting a response.  Great.

However, the response is content data, base64 encoded, tab delimited.  It should be saved as a gzip file.

I understand, I just need to create a location entry in the Dump file parameter in order to have the response get saved.  However, double-clicking on this field does not open it for entry like other fields.  I have tried Global Parameter settings, etc. with no luck.

So, how do I get this file to save?  I am using SOAPUI 5.4.0 (open source version).  See attached screenshot.