Hi Baltbirds,
If you think the leak is coming from the water heater, you should take a look at the hot water outlet which is usually at the top of the water heater, on the inside. There's a check valve that is usually plastic and may have a crack. If you can get to it, this is a repair that you can do yourself, replacing the plastic valve with a brass check valve. We have an owner-written
Troubleshooting Guide for Water Heaters that has pictures and instructions on how to change the fitting. Because your trailer is fairly new, the plastic part should come out easily.
If the leak is not coming from that check valve, or if you don't feel confident doing something like this, you might check into whether there's an independent service facility near you. If there is, you can ask Heartland to authorize them to do the warranty work. An independent shop might be less likely to have a long wait since they aren't prepping new units for delivery, and aren't spending a lot of their time fixing the warranty shakedown problems that show up on new trailers.