Cold Heat and Dust protection.
Enclose your tank in a insulating protective secondary cover to keep it out of the sun when its hot.  Reduces ammonia evaporation and extends DEF usefull life.  
Cold weather users can extend freeze tolerance or use heated blankets to prevent freezing overnight.   Universal Dust protection and a convenient place for your DEF accessories.  Velcro top seal and handy strap pockets. 
Designed to fit under a standard pickup tonneau cover.