If you work somewhere over the summer that is not your home can you claim a per diem write off for every day you are out there?

You can claim per diem for lodging (if your employer didn’t pay for it) and meal & Incidental.

There is a chance that the per diem rates may not be more than the standard deduction. Which, at that point, the per diem rates wouldn’t matter because you would take the standard deduction

For per diem rates, see this website Per Diem Rates Look-Up.