Multi Value Parameter use in Element by Expression (Before Data Trigger - Package Solution)

I have a scenario where I am looking to concatenate several parameters into a single element that can then be referenced in headers in reports.  I have it working for an RTF template, but I'm trying to do similar things with the Report Designer and am hitting a stumbling block.

Example of Parameter Data:

Parameter1:  Building A

Parameter2:  Organization 1, Organization 2

Parameter3:  LOB 1, LOB 2, LOB 3

I'd like to add a global function element that formats the element like this:

Building A//Organization 1//Organization 2//LOB 1/LOB 2/LOB 3

and the code I use in the expression function (which is slightly modified from the RTF working function) is: