This feels like a new stage of collapse for the country. Police targeting a business and literally pulling highway robberies because they know it doesn't have the political connections to protect itself.
It's funny, armored car companies are so used to working with cops they have no idea how to handle it. Why would you train your employees to tell them what they are doing?
Why tell them it's weed money though? Say the company has a lot of different clients, maybe mention some of the non-weed ones. If they press on about it say you can contact the company if you want detailed logs of what is from who and where it's all going, but it's a weird thing to ask on a traffic stop. "I just work here man."