State troopers and cross-county task force cops patrol the highways, national, state and local alike, of Texas all the time with dogs. They pay fairly close attention to the interstate routes (national highways) since those are the likely routes that drug-totin' folks take. They will find any reason to stop you if you arouse suspicion, and Dutch Pimp's right. They'll find some official reason to search you if they want to. They may not have the drug dogs right there with them at all times, but they're usually somewhere within a two- or three-county range.

You're wise to be cautious. I'm not sure that's a risk I'd be willing to take.