The electric mobile home water heater differences other than size and placement of the water connections may include lower wattage elements and a different placement of the anode to provide better access in the limited space. Many of the older mobile homes will have the electrical power supplied by a 2-pole 20 amp. circuit breaker and 12/2 cable, in this case 3800 or, lower wattage elements are required. If electrical power is supplied by a 2-pole 30 amp. circuit breaker and 10/2 cable then the 4500 watt elements may be installed. If there is room, the power supply adequate, sufficient space for anode replacement and pipes can be routed to the top a regular electric water heater can often be installed. Check with your local plumbing inspector to be sure.
The biggest difference on the gas water heaters for mobile home use is the venting for combustion air, and the exhaust vent. Older mobile homes had a air inlet ducted up from the floor into the water heater however, the newer mobile homes often have different venting which would allow the use of a regular gas water heater if the flue connection can also fit. The other differences of anode placement, water connection placement also apply. Mobile home gas water heaters are also often able to use either natural gas or, LP gas with a conversion kit supplied, regular gas water heaters typically are not convertible and the proper fueled water heater would have to be purchased. Again check with your local plumbing inspector to be sure.