Don't believe the hype-
Mexico is very friendly, as long as you don't hang out in the border towns or in Baja. All the paddling is in rural communities, and the people (including the federales ) are helpful- I've had folks run shuttle for us, help me out with car problems, invite me in for dinner. Ciudad Valles is a small, fairly clean city, and I've never had a problem with any theft or violence whatsoever. Most of the time I've camped and left my tent up in the park while we do day trips in the area. The paddling is unreal, too.
I've been down five times, mostly in January- let me know if you want some beta and I'll steer you in the right direction. Valles is about 28 hours away, so it sounds like it's in your range.