Nine years ago I designed a new style of cradle box, and it is rewarding to see the idea picked up by others. Below is recent one I made is for this stunning early 20th century French fine binding. The cradle also supports the slip-case chemise which is quite fragile. The slipcase itself is missing, or maybe it never had one.
Some other examples from around the web:
A variant from Trinity College, Dublin.
Rehousing a fragile book of engravings at Princeton University.
Display and storage for an artist book from Karen Apps.
Three different types of cradle boxes on the AIC book conservation wiki.
A simpler version made out of folding board.
A group conservation project from Duke University, with some construction details.