Having gone through the same business when replacing the overhead liners in our boat
, I found that the most effective adheasive remover was 3M General Purpose Adheasive Cleaner #08987
. It can be obtained in a spray version or in bulk from most NAPA and similar auto supply stores. In bulk one can paint
it on and, after awhile, use a small wire brush to remove the loosened adheasive. Note that this solvent is very agressive and it is important that you thoroughly ventillate the space you're in (I used a box fan) and that you used a very good quality mask rated for VOC's. Without you will do serious irreversible damage to your lungs, liver et al. The stuff proved to be the only material that actually worked out of everything I tried over a period of several weeks.