Weldwood contact cement works great for gluing in headliner material. I am not sure why people think it is not heat resistant. This glue type is the automotive industry standard that has been used for headliners with foam backing as well securing the padded landau foam for over half a century.
When you see a failure the issue is not the contact glue but instead the failure comes from what material they used for the headliner. For instance if someone used standard marine vinyl from a fabric store source. That type of vinyl is not meant to be glued and it indeed will fall
down off the walls or ceilings as soon as the weather warms up. You do need to source a material that is specifically proven to be suitable for gluing with contact cement in vertical and overhead areas.
If you don't think this glue sticks to the fiberglass like...well glue then just talk to any of us project renovators of fiberglass trailers who have gone through many sweaty hours of trying to get that residual of that stuff off the walls and ceilings.