First read about creating settings (yes, you can use ServiceProcessInstaller and ServiceInstaller in the setting)
Next, consider creating a merge module. The merge module is like a library that you can include in your customization. Thus, you would create a merge module for your service, and you would include this merge module in each of your product settings.
Edit (added instructions for setting up the merge module)
First, make sure your service is installed correctly if you are using InstallUtil (this step verifies the spelling and binding of your installation installer and the service installer code).
Then, once this works, I think that all you need to do is configure your merge module to install the service. Here's how:
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