Mike,
I had the same problem. Tried sticking velcro to the ceiling, and velcro to the insulation. Lasted about a year. Tried liquid nails, lasted 20 minutes. Tried Gorilla glue, lasted 5 minutes.
Finally, I had the piece of insulation so ruined, I just tossed it in the garbage. Posted a thread here about it, and got lots of ideas, including yours with the fender washers.
The coach is in storage right now, but when I have it out for a possible trip to San Antonio in February, I'm going to have a go at it again, with a new piece of insulation.
The biggest problem for me is getting up in there, finding something to hold it in place while I get all of the fasteners started. I'm 6' 3" and 230 lbs with replacement hips, so its a very difficult job. Lots of #)%#$#^^&#$( going on! :-/
Good luck on yours, and if you find an adhesive that actually holds, let me know, please.
Stan