How about making a one or two piece headliner that is glued/fastened in place. Like the newer cars have. You might even be able to go to a salvage yard and find one in a big vehicle, that you could trim down to size and recover...........I've done a few headliners on my flip cars, and the materials (fabric and glue) are usually less than $50.00 at your local upholstery supply shop.
