I agree with pnichols.
It's ideal if the rear tires determine the width of the rig. If the rear tires stick out, then the house could have been made that much wider. If the rear tires are significantly inset, then the rig is going to suffer a little in stability. I personally don't think a few inches will matter as long as there is not a weight distribution problem. But comparing a Ford E350 to a Sprinter is a notable difference of roughly 6", yet Sprinter owners swear they don't have trouble so maybe their chassis design compensates. I have seen the earliest Sprinters with the 5 cylinder engine swaying all over the road, but I think Mercedes made things better since the 2nd year of the V6 diesel. They may have done as OEM what I had to do aftermarket with my 2007 E350. Mine is extremely stable but it cost me extra to get there. Any/Every Ford E350/E450 with the current grill design is ready to go unless there is a significant weight distribution problem. A rear trac bar, better shocks, heavy duty versions of OEM, are all available to get the rig right.
For Visual Reference
Here is a new model of my motor home, Phoenix Cruiser 2350 built on an E350 chassis. Note the position of the rear tire to the outer wall. The wheel is just about flush with the wall.

Here is the exact same model but built on a Sprinter chassis. Note how the rear tire is deep inside the wheel well.

Here is another angle
