.dtsx vs .dtsConfig

Question

Hi,

I am quite new in SSIS Package Configuration deployment utility.   I will go directly to the problem.   We have deployed a very simple package from a specific local machine to QA environment and we have encountered an error saying that it can not acquire connection which of course right away the first thing that comes to our mind is the connection manager.  Now upon manually changing the actual .dtsx file to put the correct server and data source respectively it works perfectly fine.

My question is that we used the build utility and set up the package configuration in such a way that we can explicitly specify the connections and server names upon installing the package to another machine via the manifest file.  But going to the process of installing the package via the manifest file and entering the server name and data sources when we run the package, the package is still using what is set during the development of the package which confuses me now of what is the use then of the .dtsConfig and what is the solution for us to refrain modifying the .dtsx file everytime we move from environment?  All the way, my understanding is that upon executing the .dtsx by double-clicking the file, it will inherit what is set from the .dtsConfig file.   Is my understanding wrong and is there something that we need to do as part of the installation procedure for us to fully utilize the deployment utility?

Really appreciate very much any help or link to any mail threads that discusses the same issue.

Best Regards,

Bjorke