Instead of putting expressions in object properties, try putting them in variables. That will allow you to debug them (in Watch window) and to reuse them for other objects.
(Expressions are features of SSIS packages that allow you to assemble values of properties at run time of dtsx / SSIS package. They are replacment for Disconected Edit in DTS 2000. Expressions are set in Visual Studio when you start editing individual package. )