Yeah, those art portfolios are great for cel 
storage and displays. The closet is fine! 
However, you might considering standing those 
portfolios up right. Since you bag your cels, 
sketches, and backgrounds separately, laying them 
flat or standing them up does not matter that 
much. But better to be safe than sorry! You also 
want to make sure that your closet is nice and 
dry. Well, hope this helped a little. Good luck!