I'd stay away from the tankless water heaters if you plan to dry camp at all with the trailer.
I also recommended placing your waste tanks roughly center or slightly forwards of center over the axle, which also spreads the weight.
While you don't run out of hot water, it takes more water to get the hot water (Longer run time before hot water starts happening). Also, the more open the faucet, the cooler the water.
There was a fairly large debate on these on NATCOA FORUM
, since lot of us do dry camping and the extra water consumption wasn't worth it.
Personally, I'd recommend a good 10 gallon Suburban Propane Dual Fuel Water heater (Can run on gas or electric or both at the same time) that's manually operated. You have more water temperature control with the manual unit, and it doesn't need battery power to operate.
I also recommend the Suburban unit, even though it needs an anode, because it has a higher BTU recovery rating than the Atwood units. Also, the Suburban unit requires a smaller hole be cut in the skin of the trailer than the atwood model.