A Canticle for Leibowitz Steaminess Rating

Exactly how steamy is this story?

PG

A novel set in a monastery, in the middle of the American southwest after it's been turned into a nuclear wasteland. Sex is probably the last thing on these monks' minds. They're too busy trying to survive Lenten trails, nomadic invasions, and launching priestly rockets into orbit to bother getting steamy. Sure, there are Succubus dreams and a tribal leader with multiple wives, but that's all kept in the background—mentioned but never seen.