After gluing an airframe together, wrap it in tape. I use a thin colored tape used to wrap styrofoam gliders. By wrapping the airframe, you put tension in it to keep the sides together. Glue can keep the sides from sliding relative to each other, but tape puts the inward force on them that helps keep them together.
Uline makes a wide selection of tapes.
Avoid aluminum duct tape as it adds unnecessary weight and creates a heat shink to draw heat out.