My headliner had been a problem ever since I got the unit in '09, mostly in the bedroom.
What I have done is have a guy from the paint shop on the airport where I have the '36 parked, to come over and spray adhesive that he uses for aircraft headliners. First though I scraped and vacuumed all the old foam off the headliner material. It doesn't look perfect, but I didn't have to remove the whole headliner just the part that had come loose.
The rest of the motorhome ceiling has enough fittings, vents and ac units that prevent the headliner to drop down noticeably.
This may not be the best way to go, but it does look ok and it is not coming down in the near future. This problem is common judging from the comments at the factory when we stopped there 2 years ago. I wonder if the trailers had the same problem?
My 2 cents worth,