without an engine and an axle, the motorhome could be at such a height where you don't needs steps to enter.
The frame height of the pickup is because of where the axel, differential and drive shaft have to go.
With electric motors, you do not need to take any of that into account. (of course, other constraints come into things.)
I will have to disagree with you, seeing plenty of air lowering suspensions that take the car with a full drive-train all the way to the ground.
The in-wheel electric motors are probably what you would look for, but you still need a frame to build the coach on. And, I bet there are disadvantages to not having connected wheels.