You only risk an audit if what you claim for R&B is in excess of what you would pay if you lived on campus. A few things to be aware of though.
If you are not enrolled full time during the summer semester, then you are not living there and paying rent/food for the primary purpose of attending school . So 529 funds used during said time for R&B would be an unallowed expense and therefore taxable income to the benificiary recipient of those funds.
Generally, for the summer semester the best a student can do class-wise is two classes. But if the student is enrolled in just one class for that semester, then as far as the college is concerned they are enrolled full-time for that semester. Remember, its the college and not the IRS that defines what constitutes "full time".
