VHF needs a ground plane ideally 19 inches in diameter for the 2 meter band. Slightly less for the commercial/public safety sections of the band.
You have a decent ground plane in the tool box. May not be perfect, depending on the size of the box, but you've got one.
Ground planes are really important for transmitting. While important for receiving, a less than ideal ground plane is not going to prevent you from hearing something.
I'd really suspect that you either have a bad connection somewhere, an issue with the base/coil/whip mounting, or a bad connection.
Mounting the antenna below the cab is going to create some issues, can you try mounting it on top of the cab?
You'd need to do some testing to figure out where the failure is. Without knowing your skill level or what sort of test tools you have, I can't tell you where to start. A multimeter would be a good way to test this, if you have access to one.
Good places to take a look for issues:
Make sure the antenna base is making contact with the antenna mount.
Make sure the contacts are free of corrosion.
Check the underside of the antenna mount. Make sure the cable isn't separated, corroded, damaged, shorted to the mount, etc.
Check all of the coaxial cable for breaks, cuts where water can get in, etc. Pay special attention to where the cable enters the vehicle.
Check the connector. Be wary of any adapters.
Try connecting a temporary antenna directly to the back of the radio and see if it works.
Make sure the frequency you are listening to hasn't been changed.
If you have a separate radio, try connecting that to the antenna.
Couple of questions...
What type of antenna?
What type of mount?
How is the coaxial cable routed to the radio? Specifically, how does it get into the cab?
Did the radio ever receive anything? Or is the issue something that happened spontaneously.
Probably a bunch of other questions, but we've got to start somewhere.