Seriously, if your worried about someone take things out of your truck when you have the tube/half doors on then you need to make sure everything is locked, secured & bolted to the floor.
1. Don't take it shopping & leave it in the parking lot for hours.
2. Install an alarm that is made for convertable cars like Jud recommended.
3. Install a hidden switch that is easy for you to get to so you can disable either the starter, coil or fuel pump (if efi) or all. I did pull my coil wire off but the problem is that it is obvious what your doing & believe it or not some people catch on if they see all over town opening the hood & walking away with a wire.
4. Drive another vehicle & leave the truck at home.
5. Only have the truck to drive! Make the door & tube/half doors quick change. There are threads on this site & on Pirate. The search button is your friend.
6. Still worried! Put the doors back on.
7. Just make it hard for someone to steal your rig. You can replace the little things on the inside but if your rig is gone then
If I forgot anything chime in.