I have an RV10 under construction. I have to daughters that inquire if they will be able to bring a friend on trips. They are 13 and 15 so recognizing the weight and balance issues I don't see exceeding 320 lbs in the back seat with 3. Has anyone set up back seating for three? I'm thinking I could do a bench. I am concerned the belts for three will work fine for three kids but would be tight for 2 adults? Love some suggesting. Thanks!!