jm, my 2012 30" Lexington class c is basically the same as yours, on an E-450 cut a way, less than 4000 miles. Also have 6 new Michelin's courtesy of recall. Had the same problem of wander and constantly correcting steering. Had mine weighed and found I could lower tire pressure all around. Now running 65 psi front and 70 psi rear, and that did help a bit on the steering problem. Got the Roadmaster Reflex steering stabilizer set up and it made a world of difference over the stock damper. It does work--didn't get rid of the problem entirely, but about 80%.
Next on list will be too get an alignment with the much talked about 5 degree positive camber.
Grumpy