When you absolutely, positively cannot risk a flat, you have only a few choices. You can go with a foam insert for $100-plus or Tire Balls for more than $200, or you can go with Bridgestone's 4mm-thick inner tubes for roughly $20. In our opinion, you'll face a greater risk of experiencing a flat with the tube, but we made it through the rough 24 Hours of Glen Helen without flattening one.
Unlike more-extreme solutions, the ultrathick tubes require no special tools or techniques to install. And your bike still handles as if it has air in the tires. These tubes are heavy enough to affect the suspension and steering but are much better than riding with a flat tire, and I also prefer them to foam inserts. A bike with Tire Balls works better, but at a much higher cost and with potential installation difficulty. So if you must run tubes and don't want a flat, give the ultrathick tube a try.
Karel Kramer