it's almost impossible for the inside to get it.
it's some heavy oxidation on the outer layer.
and when you wet sand next time, use a bucket, and make sure you tape off the edges around the headlight[the body parts, not the headlight itself] so you don't make any scratches.
looks good. good job
oh, and thanks for making your thread title starting with "DIY:"
only if I was a mod...i'd clean this place up really good.
some more things to add for the wetsanding.
you should sand the whole thing 2~3 times, and use a sanding block. the block doesn't have to be a hard material, it can be just a foam pad so you wrap your sand paper around it. gets even sanding done.
after 2~3 times, rinse/wash the area and dry for inspection. at this stage you should look for "uneven" sanded surfaces and next sanding should be focused on getting the area evened out.
and repeat process untill smooth...
hope that'll help people whom are interested in body work.