The best way to keep a 43' toyhauler cool? Add that 3rd AC unit. :)
Seriously, the insulation in these trailers isn't the best by a long shot, and the main AC is just not going to do the job to cool the main part of the trailer. IMO the main AC should have been in the living area with some venting run to the garage. But even then it's going to struggle. There's a reason most big new trailers come with 3 AC's now.
Your wifes's idea will do just as you expect: you'll pump out the hot air near the ceiling, but that hot air has to be replaced by something, and that something will be air pulled in from outside: hot air. So you lose some hot air, some cold air, and replaced by all hot air. Not a good solution.
