Basically, the only difference in design of mobile home water heaters is that they are intended for installation in a very tight space and therefore they are generally smaller and have all the inlets/outlets as well as valves on the side of the body and nothing on top. I mean, this is just in very general terms because there are some larger models (by GE, I think) that are marketed to mobile home owners and yet they are still of considerable size (40Gal) and designed just as any other electric water heater out there. But, again, normally a mobile home water heater would be a smaller capacity, shorter, stubbier body with all the connections done from the side. Â
As far as the smaller wires you've described - this sounds like a sensor, likely a temperature sensor. When you have your connections on the side, you can't use a dip tube to separate the cold inlet water from the hot. This heater appears to come with a controller that takes the water temperature at the very top of the tank into consideration as another data point for switching the low or the top heating elements. This would be just my conjecture - the model number and the manufacturer's name would be extremely helpful.
By the way, was that a point-of-use heater (tiny) or something more like an actual household water heater (just small)? PoU ones have their own specifics but swapping a "normal" mobile home electric water heater would not be any different from those other standard jobs you've done in the past.