Thanks Pat, your explanations are very clear, no pictures needed to understand what you did.
I had the idea to do something like you described, but my question is : would it be easy to access if I can't really move my frame? My vintage cabinet are no larger than about 20-25 inches. Even if I don't move them, I can put a chair in front of it and have access to the top shelves. But a frame is about 30-40 inches...