Marinating pork roast overnight?

I have a pork sirloin roast, onion soup mix, salt pepper, garlic, mushroom and potatoes. I plan on starting it around 11 in the morning before I go to work and am trying to decide how to marinate it tonight? I've rubbed salt and pepper on it, along with a little garlic, should I just use water for tonight and then an envelope of soup mix in my crock pot tomorrow? Suggestions please :)