Hi Joshua,
In Visual Studio and in your project, rigth click on left button of your mouse and click "Open Folder in File Explorer" option, and then you can find your dlls in ..\bin\Debug folder.
Additionally, in the Customization.settings file, you need to specifiy like example below, so "MyCrtExtension.dll" file should exist in SDK Referenses Folder:
<!--ISV_CommerceRuntime_CustomizableFile Include="$(SdkReferencesPath)\MyCrtExtension.dll" /-->