You are missing something... Now is that the device made by Power Soluti9ons RV (PSRV) if so you misunderstand how it works....
PSRV (power solutions RV) was a comany that made a handy device which worked as follows..
It consisted of a plug, an socket and a 20 amp breaker instructions and some 12ga wire.
I will "Condense" the instrucitons here
Original wiring of a Moto rhome
"Stuff" (See below)-------------------------- Rear A/C
Modified
"Stuff"-------------Outlet/Inlet (plug)--20 amp breaker-----Rear A/C
how it worked
ON a 30 amp side you remove the outlet (on a pigtail) from the inlet, and plug the outlet end of a 12ga Extension cord onto the Inlet Plug the cord into the park's 20 amp outlet and you now have the rear A/C 100 percent independent of the rest of the house. Works great.. I built my own.
On 50 amps (As I am now) I plug the outlet and into the inlet and all is good.
IT does NOT "Trick" the EMS, the EMS just never powers the rear A/C.
And power for the Rear A/C does NOT go thorugh the transfer switch
Oh yes when you plug into 30 amps via an adapter.. Power is split between the two 50 amp HOT solenoids in the ATS, but the NEUTRAL carries all the current.