A desert racing friend of mine and 20 year motorcycle mechanic actually gave me this cheap fix.
Take an old inner tube of the same size and cut out the center strip about 3/4 inch, the area that would meet the rim band. Then take the remaining piece of inner tube and wrap it around the good tube evenly. Install both tubes together inside the tire.
What this does is prevent the tire sidewall from pinching the good tube causing a slice. Rubber pinching rubber won't cut the good tube when you hit a rock or g-out, compressing the side wall.
I have never had to finish a race with a flat since doing this and its cheaper and lighter than thick tubes or moose type tubes. Give it a try you wont be sorry.