You don't have to write off Mexico if you really want to go
Hello again. Another possibility would be to leave your American rental car in a safe parking lot in the U.S., and rent a car on the Mexican side of the border for your visit with your friends in Chihuahua. Speaking from my own experience, safety is not a huge concern as long as you use common sense and avoid dangerous situations. Personally, I love traveling in Mexico; it would probably be worth a seperate three month vacation, though the most interesting parts of the country are well south of the border area. I have an article on my personal website called Mexican Road Trip, circa 2015. It's packed with information about the border and all the red tape, so you might find it of interest.
Rick