It really wouldn't be very smart for me to announce to every would be thief how I protect my truck, but in general terms, I lock everything with high quality locks and I have state of the art alarm, security and personal protection systems installed.
As a basic but effective precaution, I lock everything with high quality locks. I keep all tempting items out of view and locked in storage compartments. I use vehicle disabling systems to make it difficult to drive my truck away; it's pretty hard to move a 10,000 pound object if it can't be started and the wheels are locked up.
I use electronic alarms and vehicle monitoring systems to protect and track the location of my truck. If a thief managed to get past my security systems, the truck can be easily tracked so it is unlikely they would get far before being apprehended. Finally, the EarthRoamer® sticks out like a sore thumb, so it is unlikely any thief would get far without many people being aware of the theft.