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
Tow PKG + Park Sense + Backup Camera + Navigation + Alpine 9 Speaker
Mopar Slush mats + Cargo, Mopar 4" Chrome tips, 1.25" Bora Spacers, 15% Tint,
Overland Black Mesh, SRT Taillight Bezels, Gorilla Black Lugs, Sylvania Ultra's