I really don’t like ranch dressing much because of the unpleasantly sweet fakey flavor. I love blue cheese. What I actually did, since I don’t have blue cheese dressing in the house, was substitute Hellman’s mayonnaise and crumbled Maytag blue cheese for the dressing. I found it to be plenty runny enough. And it contributed blue cheesiness without being a terribly strong taste in the mix. It definitely is not overwhelming.
ETA: I see I mentioned this sub before. Oh well, in case anyone doesn’t read back, I’ll leave it in.
Since it is incredibly easy to make, I can’t imagine freezing it in advance. Leftovers–If any! Not in my house! 
--would certainly keep in the fridge for at least several days and could be reheated.