You might want to think about some steel cable to use with your hi lift as a winch. I think it's far more important to have a way out than to invest money and time into something that really is an elaborate means of getting further IN. Lockers are great, but first things first.
Tire chains might also be a cheap alternative. I don't own a set myself or have experience with chains (plan to) but I've read that a set of good chains can provide a boost in traction so profound it's almost unreal. You could score both said items for less than 1/4 the cost of an installed locker. <img src="/forums/images/graemlins/kewl.gif" alt="" />