Found in Walmart - Hot Wheels "Combat Medic" van in all its ugly glory. It is available in many different color schemes, all of them just as awful. Orange windows?!?!? The shape looks about right for a UPS truck though...
Hot Wheels "Combat Medic"
Here is a real one.
After drilling out the two rivets, this is what you get. Body has been brush painted brown. The chassis was spray painted black just to get the wheels colored, then trim rings highlighted with a silver Sharpie pen. Window glass was painted flay grey.
Painting the orange window insert grey makes a more believable effect. Clearance lights are dotted on with a mini-brush.
All done... those are true HO scale figures, so as far as size goes, I say it passes the good-enough test. Lights were dotted on with a mini-brush. Stripe was leftover from a decal set, logo brush painted on. This can also be modeled with the door open if desired, it can be easily removed from the inner piece.