1. Drop a device into an outdoor HLT (Up to 12 gallons of water).
2. Plug it into 120 VAC outdoor outlet equipped with a standard timer (like you use to run your lights when you're not home).
3. Wait 8 - 10 hours.
4. Have the temperature of the water be ~ 165 - 180F.
If yes, commercially available or do-it-yourself build only?
That is a long time to wait. If you want to use a pump you could look into a RIMS tube for more "on demand" water volumes and temperature or a HERMS build but I can't claim to understand what that entails at all.