Yote- Not sure where you are, but here in the Ozarks, even with a .177 pellet gun the authorities will assume that you're poaching. I've had 2 friends who lost there powder burners when they were caught just spotting deer offseason with an unloaded gun from there trucks. One got his back eventually. The other lost a very expensive custom AR. Good luck.
I definitely understand that, but poaching is poaching. They don't care if its a rock, or a spear or your bare teeth. Like a say, great idea.
Laws vary by state. We can now hunt with air rifles so the same laws for vehicle use apply. Thankfully they havent applied all the stupid (un)SAFE act laws to air rifles (yet). Conversations like this are a good thing. They bring issues like this out in the open. Of course if too many of use do this they may but age restrictions or even outright bans on pool noodles and duct tape.
Yote,
You may want to follow through a bit more on your research as to the legality. Not knowing the state your from there may be more to this than you have considered. From the read thus far you have mentioned the legality aspect from talking to a single highway patrol officer, who may or may not know all the law you referenced too. What about the other agencies, Fish & Game, or what ever name given by your state? They often have far out reaching hands in such matters and I would highly recommend contacting them.
As a mention, in my state, even leaning against a vehicle while shooting constitutes a violation. Perhaps your state has more relaxed laws in reference too, in that case lucky you.
Cheers