I have never seen a Class C motorhome with a ATS....Not ever...It does not need to be automatic....nor does it need to be a switch. Every one that I have ever seen has a TT-30 power outlet wired to the generator into which the shore power cord is plugged into, cheap , easy, and fully complies with the code to separate the sources so that the generator cannot back feed to the shore power. This is what is done in 90% or more of motorhomes. This does not exclude the possibility of using a manual or automatic transfer switch.
I would expect that if I had a $500,000 dollar Class A motorhome that it might have a automatic transfer switch so in the case that it is raining cats and dogs I would not have to go outside and disconnect the power cord and plug it into the generator outlet, then start the generator, having an automatic transfer switch is a luxury, it is not required. In fact I have seen factory equipped motorhomes that could in fact start the generator and transfer the power automatically when shore power fails, but this is a luxury, not a requirement.
An acquaintance does if fact have a $300,000 dollar Class A motorhome but it does not have an Automatic transfer switch, that is done in the AC/DC breaker and fuse panel with a manual switch, he then needs to go to the generator control panel and manually start the generator, he can remain connected to shore power but it will not back-feed as this requirement is fulfilled in the AC/DC power control panel which also contains the DC battery charger