You could get some coil spacers that would lift the front end an inch and then not have to worry about getting the fenders painted and all that. But yes you could get the fiberglass fenders to give room for the 31's.
Although remember the bigger the tire the more loss of power you will get without a regear. 31's should be fine but 32's you will defiantly see a difference in power. Also depends what engine you have.