It's hard to compare eating on the road to eating at home, because the circumstances are so different. It's not a question of the volume of food or the calories needed, but the difference in buying patterns, types of food eaten and availability of fresh vs restaurant/fast food.

Why don't you go on a "road diet" for a week, shopping and eating as if you were on the road. That'll give you a sense of what you'll actually do, then you can scale it for the added intake.