More than likely since I am getting a better than I expected tax return I will be going with a portable that I will build into the interior and vent straight out thru the wall but another idea I had was to use a home wall unit and push it out the front of the trailer onto the trailer tongue and use some rubber bushings for vibration then fabricate a box or modify a tongue box to fold open to let it breath.
The thought is it would not take up critical floor space and mounting it low you would not have to do any special reinforcement on the wall.
Good outside the box or dumb idea?