Hello Bruce,
The Side-Sill insulation is held on with a Rigid-Type Body Panel Adhesive. It is available at Automotive Paint Stores, but do not expect to find it anywhere else. I personally use SEM Gen-Purpose Body Panel Adhesive, Rigidity: 1. It comes in a 2-part tube, like Epoxy. Tubes are Black, Label is gold, Adhesive is black. Not cheap, about 40 bucks a tube...but it is arguably the best. Other good manufacturers are Fusor and 3M... Though SEM and Fusor are your best bet.
Squeeze out equal amounts onto a peice of paper, Mix WELL, and apply. Use clamps or another type of device to hold the glue spots steady, this stuff takes 90 minutes to start to set in most cases at 70F, though warmer temps speed it up considerably (about 30 min at 90F). Full Cure in 12-24 hours. Be careful not to mix too much at once, as this stuff acts as its own catalyst in large quantities due to the heat it produces after it begins to react, which can make it set up before you are done applying if the mixture reaches 130-160F. Mix enough for 3-6 glue spots at a time.
Lastly, make sure you chip off as much of the old glue as you can before applying new. But if it is REALLY sticking, just leave it, it is doing its job and the new glue will adhere right to the old.
Any questions, let me know.
PS- I do not recomend putting the sills together with no glue. Though 99% of the time it would be fine, if somehow you lost your lower screws, or the insultion didnt fit quite right, you could take the chance of having the insulation move, and cause a fire/paint damage/heat problems, etc...
