Stove top mac and cheese in advance?

I agree with sexy on the evaporated milk being the key here. Especially good for boys on a farm drinking..which made me chuckle.

Interesting about evaporated milk. I recall sexy's question, but had forgotten, and just found 3(?!) cans of it in my pantry - no idea why, as I use it maybe once a year for pumpkin pie - so this may be the ticket.

I suggest making the bechamel - which keeps in the fridge well - ahead, then combining with macaroni on the day of, and baking in the oven, topped with buttered bread crumbs and/or more cheese. Under cook the pasta a little before the final bake, and make more sauce than seems necessary - helps keep it creamy/saucy, as quite a bit absorbs into the pasta in the oven. I've done many times and it works fine. (Well aware of pasta tradition in Italy...but you asked about mac & cheese, so hope that helps ;-)

I just read an interesting part of Food Lab (Kenji Lopez Alt newish cookbook) on mac & cheese, why it doesn't reheat well.
Have a look at this post of his from Serious Eats, for ideas and how to plan your meal.
http://www.seriouseats.com/2015/10/the-food-lab-fifteen-minute-stovetop-macaroni-and-cheese-recipe-food-lab-book-excerpt.html

PS he also has about a dozen other posts on mac and cheese, if you want to look for variations.

I just reheated it in the oven (I think 300F for 30 mins.)

I asked a similar question two years ago. Evaporated milk was a clear make-ahead winner in my book. https://food52.com/hotline/21624-evaporated-milk

Evaporated milk in a mac n cheese recipe keeps the texture creamy. Have you tried Ina;s recipe?
http://www.foodnetwork.com/recipes/ina-garten/mac-cheese-recipe.html

Melted cheese does not reheat well. For that matter, I personally do not like reheated pasta much either. In Italy, you only cook the amount of pasta that is to be served immediately; typically pasta is an appetizer course with portions to match, not the gargantuan gut-busting mountains of pasta that Americans eat.

For the sake of quality, I suggest you find a way to make your mac and cheese shortly before serving or find something else to serve.

I would never ever serve reheated cheese to dinner guests. Heck, I won't even eat it myself. But it's your call since it's you and your guests who are going to eat it, not me.

Good ulck.