If you are planning to take your Toyota FJ Cruiser off-road the installation of trail armor is of critical importance. You can get protection for most of the critical under body components. Of primary importance are the front differential, oil pan, transmission and transfer case. You can also get protection for the read differential, gas tank, and the rear locker activator.
Here is a comprehensive list off all the under body trail armor for the FJ Cruiser. Were possible I have included reviews of the components by people that actually are using them on the trail.