bed sides

[2tankin79]

Hey, on www.usbody.com they have some fiber glass bed sides, and say

73-87 Fleetside Bedside...
Features:
- Smooth grey gellcoat exterior finish - Fiberglass textured Black
Lacquer inner.
- Skin Only - Will not bolt to stock location

skin only-will not bolt to stock location??
what is "skin only"??

also, what would it take to fill in the tail light holes? seein as how i have a rollpan with corvette tails, my stock holes etc are gone for the original tails, and not sure how i would go about filling the holes for the lights on the fiberglass.

thanks, Jeff