jgrason, I have company coming over tomorrow night and have decided to make this crumble for desert. The recipe looks pretty straight forward but I've got a couple of questions. If I prepare it today, do you think that it would be alright for tomorrow? If so, would you refrigerate it? And lastly, flavor wise, in your opinion is it worth the effort to bake it on the grill? All opinions are welcome.   

Per a comment in the recipe notes, I substituted 3 cups of diced peaches for half of the blueberries. The Traeger is set to 360° and the crumble will go in as soon as the temperature stabilizes.

Definitely refrigerate overnight and reheat before serving if you want it warm.

No issues with 24 hours.  Not really something that would go bad in 2 or 3 days, even with the sugar content.  But I am the guy that likes cold fruit, where I think your average crisp eater is going to like room temperature or even warm.  Although, the warmth can be easily added.