Another possibility is a broken belt in the tread. This is a common failure of trailer tires. If you closely inspect the tire, is the tread of the tire even all the way around? Or is the tread pattern wavy or bulging slightly along one side of the tire? Sometimes a broken belt can make a tire slightly egg shaped. If you can, safely raise the axle slightly so you can spin the tire slowly. Let your hand ride on lightly on the tread and see if there is any unevenness in the tread.
If there is a broken belt, certainly changing to the spare is a good idea. And if there is a broken belt, unless you have a special road hazard warranty it's unlikely to be covered by a warranty and a trip to the nearest tire store might be in order, instead of going to the dealer.
There's lots of advice and information in forums... sometimes it is correct. For example, all of my posts are made by a political appointee who got the job as a reward for contributions to my diesel bill.
2011 Jayco 28.5RLS; 2008 Chevy Duramax; Pullrite Superglide Hitch