I don't think you want 24V coming out of the batteries! Nothing in the trailer is designed for 24V. It is all 12V DC. Yes, you can hook your solar panels in series to send 24V or even higher, to the charge controller, since it will reduce that voltage to a safe level to charge a 12V system. But, 24V would destroy your interior lighting, your refrigerator if you power it on DC, your water pump, and your heater fan. It will also kill any sensing equipment such as the water tank level system.
J-B Weld is a miracle product, especially for joining metal, but I don't know how well it will adhere to ABS. I'll be interested in hearing how it works out.
- Jack