AC unit is heavy, trailer would have to be built with the structure intended to handle the weight
. If not the roof would collapse or walls would bow out as trailer was squished like a balloon.
A lot of people put small home window units in. The install them through wall under rear dinette table supported by rear bumper, in a closet vented to the outside with unit coming through closet door or replace a window with an AC unit. Or come through the front using the tongue to support it. So there are options.
I have family in Kansas, made many trips out there camping for family visits so totally get wanting AC.
I suggest taking on one thing at a time, fix that and move to next thing. Windows
sound like a good choice since that would make working on it more comfortable.
Post some pictures, only so many types of windows
used in these things you will probably get some good advice on how they work, where to get parts etc.
Suspect window originally opened, something broke and rather than repair properly prev. owner just sealed the window. My front window was caulked and screwed shut with two small screws when I got it, owner said he could not get it to be rain tight since the latch was broken.
What does in and out handle mean? If this is the one in prev. pictures that looked like a twist handle. All replacements would have keys. But should be aware that if you remove the two hinge pins and you can just lift off the locked door. Not terribly secure.
You might check out the thin white plastic 4x8 panels sold at big box home improvement stores. They bend, don't know if you can paint
them. Another approach is to make many shallow cuts with a saw from top to bottom on the back of a wood panel to make it more bendable. That is something of an art to get right but it does work.
Bolts that attach hinge to trailer or hinge to door can be loosened which allows hinge to be twisted a little bit up or down to get better alignment with opening. You use "warped" to describe the door. Do you mean not curved to match the curve of the trailer wall? Or crooked/cocked in opening?
square foam insulation of about 1/2 inch by 1/2 inch is what scamp
uses as a door seal, goes on trailer and door closes against it. It's 3/4 inch thick foam at the bottom of the door. So in effect door appears sort of warped if compared to opening right from the factory because the bottom does not come in as tight against the trailer. No idea if Minit is the same way.