I hope you get a better answer than I'm about to type. If so, I will learn also.
When you go to print, run a script that looks at the contents of the containor field.
If it "IsEmpty", go to a layout where there is no containor field and print that layout.
If "not IsEmpty", go to a layout where there IS the containor field and print that one.
It would be better to have one layout sliding...but I don't work with containors often enough to have faced this one before.
Again, I hope for a tidier answer than mine.
There's a hidden "gotcha" with container fields.
Enter layout mode, select the container field and use Format Graphic... to change the alignment to Top, left.
Now it will slide.
Thank Raybaudi, I learned it from him.
Thanks a lot. That solved my problem.