Carpet glue and all the others have not worked in the past for me. Once the summer heat comes it will be sagging again.
The best ive used is fibre glass resin (with activator) and lightly paint brushed on thin layer.
Has not unstuck. Just dont use too much or you will screw up the material.
You also need to remove the yellow foam under the material.
I dont think newton commercial to mk2 headliners but their carpets are spot on
