Concrete paved interstates are generally cupped from weight of heavy trucks and effects of weather. Some RV'ers claim that their rigs ride like SUV's after they spend big bucks on air bags, rear spring mods, and special shocks. We stop every hundred miles or so to relax and collect our wits when riding on concrete washboards. It's my theory that tire failures are more likely when riding on such roads in hot weather.
Allynnc, recommend you don't use valve extenders, get solid metal long valve bodies like Tire Man, Borg or custom made ones at a pro truck tire shop. Vibrating extenders on rubber valve bodies can cause rubber to crack and deflate tires causing tire failure, damage to underside of RV and possible loss of control.