The biggest disadvantage to IFS is immediate and drastic alignment shift with changes in ride height. On your P-30, if you added weight to the rear of your RV that changed the ride height the front alignment would go negative on the camber and should toe out dramatically. The result of this is tire wear. Adding weight any where on a straight axle vehicle does not change the alignment just the position of the steering wheel in relation to straight ahead. Ride is secondary to tire wear on vehicles that have drastic changes in load weight and load location.
Randy