8 to 10 mpg would be dream mileage if you had a comparable sticks-&-staples Class C. Our Class C (22 ft long bumper to bumper) got 6 to 8 mpg depending on the head wind.
Buses get a lot quieter once you start adding in sound deadening stuff like insulation, walls, cabinetry, soft furnishings. School buses are noisy because they have nothing but hard surfaces on the interior.
A school bus will take you down gravel roads with no problem. I would not do that with an RTS. We looked at an RTS in Maryville, TN. It was on a dirt road with a long dirt/grass rutted drive. David drove it down the drive and I watched. It had really low clearance. Since we tended to stay mostly in public parks (at the time, National Forests), that knocked it out of the running.
: Although the winding road leading to the campground is not RV friendly, the payoff of landing a night in this environment is pure delight.
Wildcat Road is curvey, gravel one-lane road with turn-outs, not RV friendly.
NOTE: Wildcat Rd. is gravel, steep (in places), single lane with
turnouts. There are minimal potholes and washboards.
Do you get the idea this is not for RVs? Well, not for sticks-&-staples. They tend to be too low to the ground. Popular with folks with 4WD vehicles and pulling SHORT trailers with flipped axles.
Tallulah River Campground
Good, hard-surface roads until you reach Forest Service Road 70; expect narrow gravel road that is crooked and steep in parts.