Hi Tree14,
People who have had early life tire failures usually go through similar frustrating steps. Maybe I can save you some time and aggravation.
First, the tires are warranted by the distributor, not by Heartland. So Heartland will point you at the distributor for warranty. The usual path with the distributor is for them to invite you to send the damaged tire back to them for inspection. They will likely tell you that they found no defect, but are willing to give you $100-150 as a goodwill gesture. They will not pay for any damage to the trailer.
As an alternative, you may want to report the issue to NHTSA with complete information including the tire numbers stamped on the sidewall, and make the tire available to NHTSA for inspection. If they find a manufacturing defect, they can order corrective action.
You'll likely be putting the spare on and buying a replacement tire. You may want to replace all 7 tires, especially since you don't trust the tires any more. No need to wait for a 2nd incident. Be sure to check the load capacity (lbs) of the new tires, not just the load rating.
Your trailer collision/comprehensive insurance should cover the cost of repairs to the trailer, less your deductible.
Btw, even the best tires can fail. A few years ago one of our Goodyear G614s threw its thread, taking out the j-wrap and fender.