If you did the work, you're entitled to payment. It appears that you may have actually been an employee, rather than a subcontractor. So, you may want to contact the State Division of Labor Standards Enforcemt and let them handle the entire thing. See http://www.dir.ca.gov/dlse/HowToFileWageClaim.htm.
You could also sue the contractor in small claims as if you were a subcontractor. But, you'll have to prove a contract between yourself and the contractor, and then you'll have to collect. Whereas if you file the wage claim, the State will do everything, and they will fine the s*** out of the contractor, for messing with you.
If your trailer was damaged while using it for the benefit of your employer, you could probably sue in small claims for that, too. But, it may be more trouble than it's worth. I'd start with the DSLE and see what happens.
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