What color is it painted? With 8 coats you could start with 320 on that thing!
You can let it sit opened up with the 800 scratches in it. Put her in the sun if you can to try and get the solvents out.
A trick I like to use is to sand in a different pattern for each grit. Example make X's with the 800, then do circles with the 1000, when you don't see any more X's your good. Then go back to X's, then circles, etc. A good PDR light is your friend...
