Friends recently replaced the water heater in their mobile home.
They had to buy a "Mobile Home" water heater.
I looked at the installation;
It LOOKS like a normal size water heater.
It runs on natural gas.
I know that in years past, some mobile water heaters
( electric ) run on 110 volts only....
( gas ) run on LP only.
Other than that, what's special ?
Why couldn't a regular residential gas water heater be used ?