Taking off while the other occupants sleep

In a class C motorhome the front passenger area is a "vehicle" and the back area is a "house" so most LEs will ignore the "house" portion. In class A motorhomes only the front two seats are DOT legal seats for automotive use. Also, while many new motor homes come with seatbelts in the back most of them are not in DOT legal seats nor have DOT legal anchorages. Our first MH we had a nightmare of a time with the car seats for the babies. I do believe it is a good idea to remain belted when seated. That said for the OPs situation it can actually be safer to have a rested driver and less chaotic drive because people are fully rested. Some of us working stiffs don't have the luxury of watching every flower and leisurely wakeup times in the morning. Sometimes we just have to get to the destination especially if we are returning to work. It is very different getting into a crash in a 26,000# motorhome vs. a 2000# smart car. That amount of mass will slow down and or stop much slower than a smaller amount of mass when hitting an equal sized object. This is just physics. The net effect for passengers is less effects in a crash. In our RV I used the airline rules. Belts on if you are seated and you can only get up for a short time such as to go to the bathroom or get a drink from the fridge. I would however consider what the OP did if the kids and DW were still in their beds and I intended on beating traffic out of a city in the early AM.