The basic guideline is the number of people traveling in an RV should be limited to the number of seat belts. However, New Hampshire is the only state that doesn't require adults to wear a seat belt in any seat. As long as you have enough seat belts in the RV for passengers under age 18, you'd be within the law. As for the rest of the US and the District of Columbia (DC), laws vary for front and rear seats and passenger age restrictions. If you're taking a trip in an RV, check the laws in each state where you'll be traveling.