Tool box... Is it steel, or aluminum?
Depending on how high and far from the cab-
Depending on how well the tool box is grounded to the chassis "ground" of the truck. The more physical grounding area that is capable the better the chance of the tool box becoming part of the ground plane of the truck. -
Depends on what you want out of it.
Depending on if the people that you are talking too is.... oh, lets say in front of you and you are following them and just as they crossed the yellow light and traveled a few hundred yards more before they realize that your not behind them and you can hear them but they cant hear you doesn't bother you.
The highest and most center of the vehicle. The better for well balanced omni directional signals.
I loved my 8' "Francis" fiberglass (blue) wip mounted on the rear passenger side... Just above and slightly forward the wheel well, of my 1978 FJ-40 Landcruiser.
It won a lot of bets ($) out performing lots of "center mounted, whip like" antennas. If I was next to someone and we both were talking to the same station....
Then sorry "Wilson" people. My "Directional" abilities that I had versus the nice all around well balanced "Omni Directional set up. Did me well. Using the same radio.
Used to STOMP!
See, it all depends..