Lots of great boondocking spots in many states. It all depends where you're headed. A few examples; Guadalcazar, SLP, San Miguel de Allende, GTO, Yurecuaro, Mich, Leon Guzman, Dur, Mazatlan (Isla de Piedra), Sin, Los Lirios, Coah, Bustamante, NL, Galeana, NL, Pena de Bernal, Que, the list goes on.
As I have stated before, people shy away from the border saying they want to "beat feet" across are greatly mistaken. With the exception of northeastern Tamaulipas, the border states including Chihuahua, Coahuila and Nuevo Leon are much safer than many Mexican states where rvers spend the winter. Think about it.