The trucking company is liable if his load it not secured properly or has a leaky load which it sounds like to me. If they have on their tailgates to stay back so many feet it doesn't mean anything. It is just a way for the company to blame you but it really does not mean anything and will not hold up against the DOT. If you have all the companies info I would file a police report with the state and they could get a ticket if you have proof.