Right now you have no concrete knowledge of what is going on at your warehouse. You are in no legal jeopardy right now. This will change if you inspect and find what you expect to find. If you inspect you must act on what you find. There will be a paper trail (your notice to inspect) and if you do nothing, after inspection, you could be indicted as a co-conspiritor.
Spend the extra money and have the sheriff or police serve the notice. They may solve your problem for you.
John (not a lawyer) from Hawaii (but I am a landlord)