I had another thought to add. It may to smart to allow both the pasta and sauce to cool before combining and refrigerating. That way the sauce won't further cook the pasta until you heat it the next day. Good luck!
Cooling the sauce makes it congeal which makes for difficult combination the next day. I slightly undercook the pasta and combine the two before refrigerating. And when there are leftovers, deep-fried mac-n-cheese squares are quite the popular snack/hors d'oeuvres in these parts.