"Driving a Sidecar Outfit" by David Hough.
David Hough used to write the Proficient Motorcycling column in the USA's "Motorcycle Consumer News" magazine, and has two books of that title in print (Proficient Motorcycling, parts 1 and 2, or something of that ilk). He's one of the best writers I've ever read on the topic of motorcycle safety.
I haven't read his sidecar book, but I do own part 1 of Proficient Motorcycling and have read parts of part 2, and if the sidecar book is half as good as PM, it'll no doubt be one of the premier texts on the subject of safely flying a sidehack.
Just this guy's opinion...