How to properly use class from custom DLL project in 'Assembly-CSharp-Editor'

Hi all. Well, Unity refuses to keep my custom DLL project within its .sln file and drops it after restarting. So I decided to create my own solution which contains my own projects as well as default unity projects. But now when I add reference to my custom DLL project (let’s say ‘Base.dll’) to ‘Assembly-CSharp-Editor’ project Unity drops this reference each time it compiles ‘Assembly-CSharp-Editor’. As result I’m unable to use classes from ‘Base.dll’. Does anyone has good workaround on this problem?
Thanks in advance.

Ok, I found the solution. The output path of custom project just should be changed to Unity Assets folder. Then unity will add reference to custom project to all its default projects. Fairly simple. Sorry for trouble.