Consider starting an LLC and working under that. The customer hires your LLC, not you personally. In the event that somebody needs to be sued, it is your LLC, and not you personally. If the LLC has no assets, it can simply go bankrupt and ignore any debt or judgements against it. It would have no effect on your personal debt or credit.
You can start an LLC online for about $50-150.
Really? If the LLC has no assets, who owns the tractor and equipment? I you own the equipment personally and provide it to the LLC, seems to me the owner of the equipment used "negligently" by the lessor (the LLC) could be liable. I'd not bet the ranch on an online LLC or any other legal advice provided by anyone not qualified to practice law in your jurisdiction.