I just sanded them down to the yellow, primed them, wetsanded, and then painted them. When you paint them, be sure to use a flex agent. But, I would stay away from any of the stripping stuff because it might warp them or something.
Before I start, you might want to goto google and search for "How to wetsand". You might find a page that will tell you better than me and it might have pictures and/or movie clips?
With my ground effects, I spent a lot of time wetsanding them. I used these tools,
220 grit sandpaper (I think it was called wet sand by 3M)
Garden hose
Bucket with warm water
I got the ground effects wet and then used the sandpaper to remove the old paint, down to the yellow. When the sandpaper would get dirty, I would rise it off in a bucket and when the GE would get black/dirty, I would use the hose to rise it off.
In some areas I just "feathered" the old paint out. When I thought I was done with an area, I would get my fingers wet and would feel the ground effect for a super smooth texture. My fingers would just slide over the area when it was wet.
Just watch that when you are wetsanding that you go left to right with your fingers pointing "up". If you sand with the direction of your fingers you will get an incomplete sand, where your fingers were. It will look like claw marks because the pressure will only be on a certian area for a while.
Overall, I am not good at describing things in text. There has to be a good website out there that would show you a lot more.