FYI, my dealer would NOT install a second air conditioner, even though I offered to pay ANY price to have it done. If the trailer is not pre-wired and a 50 amp, adding a second air conditioner will require some creative work.
I even considered running a separate electric line to plug in with a standard 15-20 amp cord directly to the electric pedestal. My dealer said, "no". I suppose it was a liability "thing" for them and maybe the manufacturer's specs on the camper. So our option was the 15,000.
It sounds so simple, just add a second air-conditioner. But the reality is, its not simple at all, especially if your camper is 30 amp and not pre-wired for a second air conditioner.