Pop the rear window and run some rope or bungees around the frame and secure it under the rear somewhere.
You should be fine as long as your not driving long distance or on the highway.
2015 Altitude - Billet Silver
SRT Taillight Bezels & Black Grille Mesh, Black Gorilla Lugs, Sylvania Ultra H11's,
Mopar 4" Chrome exhaust tips, 1.25" Bora Wheel Spacers, Polk DB Center,
15% Llumar Tint, Mopar All Weather Mats + Cargo liner