I'm not sure where your ATS would be located, but mine is really close to (just over) the generator & the shore power cable, which in the Sun Voyager 8351 (gas) is in the bottom of the rear closet/dresser drawers. It is impossible to see without mirrors. I'm not sure how I will access it for repair or replacement - obviously, the unit was installed before the cabinet or coach rear cap was installed.
The unit is similar size to the converter, with lots of heavy wires attached. It is just a "typical" electrical box, maybe 8"x8"x4" high. I have pictures, though unfortunately not here at work. Mine is labeled (with a cheap label) "Lyght Power Systems", though I think GS uses other manufacturers as well.