class B motorhomes

I own a class B MPV TAHOE 196 RBS motorhome, it came aquipped with single rear wheels and is on a FORD E350 chassi. It has a floating rear axle that is supposed to be capable of taking dual rears. I have had an issue with getting tire stores that sell wheels to measure the distence within the rear tire area and was avised today that singles should be just fine. The home is 19ft long, it has a slide out and comes aquipped that the generator and rest of the items found in larger C class homes. My concern is how the wind affects the body with single wheels, I had figured that duals would fit but, MPV put a light medal plate just inside the rear frame just outside the springs that limit access to fit a wider set of duals within that space. If i cut the metal to allow access would it hurt the under carriage in any way. This metal is a box type affair that covers the top and ends to prevent rocks from being tossed into the body above and front and back of the wheels, The hight of the home is the asame hight as a class C. I was also looking at an anti sway bar instead of the duals.