INSIDE FRONT COVER
Inside front cover: A nice illustration of Doc and Clea by Craig Hamilton.
INSIDE BACK COVER
Inside back cover: Lots of stuff. Upper left: Bill Sienkiewicz sketch. Upper right: Charicature by Wong. Second row (left to right): Charicature by Beau Schemery, sketch by Walt Simonson, and a sketch of Dr. Fate and Dr. Strange by Bernie Wrightson. Lower sketch: A rare illustrated letter by Steve Ditko for Roy Thomas' Alter Ego fanzine.
I always use the original back cover on the customs.