Gluing the back to the sides:

The way I, and others, glue is to put hot hide glue on both surfaces. Let it dry, clamp it together and the loosen on or twoo spool clamps a time and reheat/moist the glue with a hot knife that has been in almost boiling water.
This way you can control that everything stays where it should stay and its slow and relaxing. Two important words for me these days.