The hot water heater being on the door side is less than ideal - I couldn't agree more. Unfortunately we've run out of space for it on the off door side mostly because of slide-out placement and the 1/2 bath. You have my word that we will always try and locate those type items on the off door side as much as possible or really whenever possible.
Tom, on models where the water heater is on the door side, you ought to provide an access panel to get to the back of the unit.
A number of us at a rally last Spring helped another owner with repairs on his Landmark's door side water heater. Because there was no access, we had to remove the water heater. After putting it back in, there was additional work on some of the heater's water lines. In order to reach them we had to remove the battery compartment and framing.
Had the unit been on the off door side, those removals would not have been necessary because we would have been able to reach the back side of the heater.
I'm sure the engineers won't find it easy to provide access, but it's really needed.