Ted, Heinlein didn't write slam bang adventures for Del Rey Books. Most of his career was before Del Rey existed.  His publisher was Scribner's for many years, including all those famous juveniles in their first appearances. They were all hardcovers.  Del Rey may have published reprints long after their original publications, but his paperbacks were from Avon, Signet, and others, possibly a few from Del Rey toward the end.

And as for the question about why he wasn't asked to write ITCFOS, why wasn't Ray Bradbury asked to write DESTINATION MOON? 

Last Edited By: Monsterpal Aug 11 10 3:33 AM. Edited 2 times.