ive got some stock skirts that i need to repair some deep scrapes in, before i paint and install. what type of filler do i need to use on the stock material so as to last?

stock side skirts? If they are flexible, then evercoat makes a flexible polyester filler for that. You need a hardener for it also. Mix, spread on...Wait an hour for it to harden. (the polyester takes a while to harden) Sand it with 180 grit sandpaper to get the high spots, then finish up with 320grit. If you went too far, mix up some more and repeat until you're satisfied. Then you need a finishing filler/putty. we use a evercoat one that I can't remember the name of. Apply it, sand until it's smooth(being sure to overlap the previous aplication of the polyester by at least 1 inch all the way around the area) The finishing putty is much easier to sand smooth, and makes a very smooth base for primer. Prime, and get more than enough coverage for the surrounding area. Sand smooth with 320, then paint and clear. Good Luck!
Edit: Be sure it's at least 70 degrees when you're doing this(preferably inside a warm garage)