In reply to the question about Smoky checking the interior of a big rig; ICC rules and Smoky's have a way of making things into bigger things, if you get my drift. Sometimes the truckers don't make friends in law enforcement, but LEO's have the upper hand in being obnoxious.
As for the OP, if making storage is your goal I say go for it. I've made a hidden panel in a couple rigs to store papers and $$$ in--even to carry a firearm for my protection. I've never been stopped by LEO's to check my trailer and I can't recall anyone that has been. Now, I do have a small circle of friends, so what I just wrote might be slighted somewhat.