Most of the TT you mention are sold factory direct and don't have dealer network other then Airstream. The purpose of buying a higher quality TT is to avoid the dealer. Other places can work on them beside the factory. I suggest you go to the owner's forum of each mfg's your interested in and they could tell you about what they do for service. Keep in mind the warranty is only a year anyway. You can also do most minor repairs yourself. I do not know your skill set.
There are also blogs such as Interstellar Orchard where people full time in small TT like her Casita. She explains what she does for service.
