Given the preferences you have stated, the device you want is the Unified Tow Brake
Or use something like the Roadmaster 9060 Brakemaster, which has no electronic components at all in the toad.
However, I think you are worrying about a non-problem. Either the Roadmaster 9700 or Brake Buddy would do a fine job for you if it is a potable toad brake that you want.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL