From what I can tell people are using 3 channel with the rear servo turning the rear wheels in opposite direction of the front in standard mode and this site has a mod for a 3 position toggle to lock out rear steering or switch the rears to turn in same direction as the fronts for "crabwalk". I can't tell you from experience because I haven't gotten to the point of actually having a running truck.
http://thecrawlerstore.com