not too experienced here, but how about those portable vaporizers that look like a walkies talkies?
I know when ive seen them for the most part i didnt know what the fuck they were, so i doubt a cop would be able to spot it and connect the dots right away.
also when ive seen them in use, there was only a light smell, and really not any risidual vapor that would raise any red flags.
although im sure they cost $100+ as apposed to $20