To make these Peachy Keen Bars gluten free, replace the white cake mix with a certified gluten-free white cake mix. Also confirm that the vanilla extract and any packaged peach products are certified gluten free if needed for strict dietary requirements. Because gluten-free cake mixes can vary slightly in texture, the crumb mixture may seem softer or drier depending on the brand, so adjust very slightly with a small amount of butter if needed until a crumbly consistency forms.