Weldwood contact adhesive,comes in a quart can, maybe smaller - you won't need more than half if that. You paint it on the backing board only, let it tack up for 10 minutes. Have a friend help you set the headliner fabric down evenly on the backing board and roll it out smooth with a 2 liter coke bottle. Don't put any directly on the headliner material foam - it will quickly melt and harden the foam and screw up your job. The adhesion from the backing board will hold it plenty well. Oh, it will get you high quick - make sure you apply it with plenty of air flowing and no gas water heater nearby. Kaboom.