You are also likely being billed for lost rental time while the trailer is repaired.
You might start with a demand letter to the company that caused the damage. The first step to a lawsuit, if it should go that far, is simply asking them to make it right.
Indicate in the letter what happened, why they are responsible, and how much the damage is. Include a copy of the bill from Home Depot so they know you aren't making up the number.
Indicate in the leter that they have 10 days respond, then patiently wait.
Despite their sign, you can make them explain to a judge why they are not responsible for the damage they caused of they refuse to pay.
You may end up having to pay the bill, since you were the responsible renter, then seek your own compensation separately.
Take the time to identify the party registered for legal service in your state and send the letter there. This will typically be the owner or possibly an attorney. This will prevent your letter from being handled by a mid-level button pusher too afraid to let the boss know what really happened.
Look it up here:
Registered Agents