Have the coach weighed with it loaded the way you normally travel. If the front axle is lightly loaded, that can cause some wandering. Most vehicles drive better with the front axle loaded close to maximum.
If you do get the alignment adjusted, do it with the coach loaded the way you normally travel. This puts the ride height at the normal driving height and will make the alignment more effective and accurate. Have them check the thrust angle as well, which is the alignment of the rear axle to insure that the coach is tracking straight down the road.