In your case you put a false floor in and had a hidden compartment such as smugglers use. That's a lot different than someone installing a safe. As far as a couple of 20's under the floor mat it would take a real stretch of the imagination to figure that was illegal. I had an experience a few years ago when I was traveling alone and ended up having a medical problem on the road. I had to call 911 and an ambulance was sent to get me, I was not conscious when admitted to the hospital. A state trooper had gotten my pistols and came and asked if there was anything else I needed to have safeguarded. I tried explaining where a few thousand dollars was hidden and had to give up. He never blinked an eye about the money being well hidden and ended up coming back for me after his shift was over and taking me and my pistols back to my rig