It is true that for OPC "Classic" specifications in a networked environemnt, configuring DCOM (Distributed Common Object Model) is a challenge, especially if security is a requirement. With enough knowledge and proper information at hand, it is possible to set up DCOM for OPC correctly. There are various materials that can help you with this task.
We suggest that you learn from this video tutorial, which gives you 5 steps to follow for DCOM configuration.
We can also recommend Software Toolbox DCOM Tutorial.
You shoud also consider switching to OPC-UA (Unified Architecture), which is not based on DCOM, and is more firewall-friendly as well.