Not an AD - but we reworked the interior on my el camino - and I can address a couple of your questions. http://www.wsu.edu/~rsain/elco.html
We stripped the car bare - then layed in jute (that's your padding). Cut it to fit (with a little extra) then sprayed glue down on the floorboards (not the whole thing, just half of one side) then shot glue on the jute, let it tack. Now stick the glue side of the jute to the floorboard. Repeat process working out to the doors - now do the other side.
Carpet was basically the same - except that we did it in one piece. Worked from the center out - with glue now on top of the jute and on the bottom of the carpet. I would glue everything down - period.
If you need an access panel - you can just leave that area unglued and cut a couple of lines in the carpet - then do your velcro idea - now to access battery just lift a small section of carpet/jute and the rest stays in place.
I have not used the prefit stuff - ever.
We get carpet from an upholstery shop (do not use the stuff at Lowes, Home Depot, etc. - it won't flex correctly). It takes time to get over the humps and up into the corners - but you can do it.
Remember to make relief cuts (or sewn darts) to keep it from bunching up on a compound curve.
Hope this helps a little - best adivce I can offer is to make sure it is GLUED DOWN THOROUGHLY - you don't want it to creep on you....
- Ryan
