Funny, I had the exact same question but I’m far enough away from the headliner that I haven’t worried about it too much. I was thinking maybe some kind of button snaps might be interesting if I could secure them on or through the headliner.
I thought about Velcro also but I don’t think the glue on most standard strips will be strong enough and will probably want to peel off on hot days in the sun.
I’m curious to see what others come up with while I continue my build. I don’t like the idea of permanently gluing that much foam to something that will need repairs, modifications, and enhancements in the future.
-mike