It is ok to leave the coach plugged in during storage?
(This information is for a Travato with AGM batteries, not the Lithium powered units.)
The converter that WGO uses on the Travato is a smart charging microprocessor based system that continually monitors the battery conditions. When batteries are fully charged it has a trickle charge level to maintain batteries.
Therefore, it is perfectly okay to leave the coach plugged in during storage.
Conflicting information that may be in your Owners Manual was likely left in there just to protect the customer that would have lead acid batteries and who does not regularly monitor water levels as the water could boil off with excess charging. Except for the Lithium models introduced in 2019 the Travatos have AGM batteries (which are sealed units) so water loss is not an issue .
How cold should it be before I need to worry about winterizing?
When actively using the Travato, a good rule of thumb is to have the night temperatures not get below 28 degrees (F) at night, and daytime temperatures at or above 50F. If your Travato has all-indoor plumbing (K models, and newer G models) you may be able to go a few degrees cooler. Some Travatos are equipped with waste tank heaters. Those will help too, but the plumbing from the tanks to the waste port can still freeze and cause damage.