I think that rubbing will be an issue even if you change the backspacing or add spacers. Fender / Liner / mudflap trimming will be required to avoid rubbing but it is easy to do. The bigger issue is; the tire contacting the UCA, which 285's will do. Changing the backspacing or adding spacers will take care of that.
There are a few threads about trimming the fender liner to put the 285's in, no biggie!