The USPS mail delivery vehicles (called LLVs or Long Life Vehicles) have aluminum bodies/boxes, and are on chassis based closely on that of an 80s model Chevy S-10 Blazer (with some mods to give a tighter turning radius, etc). Interestingly, one of the most notorious faults of those trucks (aside from lack of A/C, poor heating, crank windows and poor traction and general ride and handling, especially at higher speeds) is that the edges of the windshields can be leaky and so can the windshield washer system. Both can leak into the electrical system and fuse box, which has caused a significant number of fires and has become somewhat of a running joke among those who've operated them.