Thanks for the input, Russ and Thomas.
Okay, I'm giving this back to Mandy by making my own comments on air conditioning in trailers.
A lot of people do it; but, having an air conditioner on the outside not only means having to carry it and put it into position each time but also leaves some other areas of concern. There's the thermostat problem mentioned earlier in this thread. Then, there is the issue of water and electrical grounding. Is it really safe sitting on the ground? (Keeping it in a plastic milk-type box may solve that problem, I don't know.) But, what if there is an unexpected rainstorm and the unit is in use outside? What if kids start snooping around when you aren't there? How secure is the ducting system? Could a kid pull it off? Is it possible that the unit could get "ten-finger discounted"? (Just a few thoughts to consider....)
Mandy, if you decide to wait to see if you need it, you could still plan for it. You could build in the extra internal wooden support braces needed based on the unit you might get. (I'm guessing it would be a small window type of unit based on a standard window size.) If you are using solid plywood walls instead of sandwich walls, you wouldn't even need to do that ahead of time. If and when you get one, all you'd have to do is cut away the extra material where you've already got the braces, frame the hole and slip the unit in.
Barb's setup is a clever add-on solution that gets away from the thermostat problem and the need to add wooden support braces in the walls but it looks like you still have to carry it and slip it in place each time. If space is limited, this may be a good avenue.
Summing up, I believe that, if at all possible, the unit should be mounted on the trailer somehow but you can probably find a way to plan for it and still not put it in unless you're certain that you really want or need it. That also has the benefit of saving money for your actual build, should you need it. As long as you've planned for it, you can always add the unit after your build is usable...or not....
I hope this helps you. Thanks again for letting me highjack your thread for a little while.
E-Hugs and Good Wishes to you
