Can't you find a 10 year old to program a thermostat for you?
I've never done this so I might be in error on some of it but it might get you thinking in the right direction. Hopefully an a/c guy will chime in.
I wouldn't go with a timer. You don't have any control over the temp with that. It could work if the outside temps and sunshine were the same every day and night but that's too variable. You'd end up having to mess with the timing constantly when you should be out hunting. It will also shut off the fan and you don't want that.
This can be important: Some window a/c's are set up so that if the power goes off, it won't come back on automatically when the power's restored. You have to manually turn it on. That will preclude the use of a line stat. I have a window a/c like that. It has a reset button in the end of the power cord. I don't know if replacing that with a regular plug would make it come back on or not.
If you haven't done it, you need to remove the existing stat from the a/c. If you can find a stat to wire in in place of the original stat, you've got it solved. A line stat, that's one that plugs into an outlet and the a/c plugs into it, would work but it has some problems. It would shut off the a/c if the existing stat is outside the trailer as you say but when it shuts off, it shuts off completely. You need to keep the fan running all the time to prevent freeze ups. That's where the Coolbot comes in because it will both override the a/c stat and prevent freeze ups. Many a/c's have an option to keep the fan running full time or to shut it off between cooling cycles to save power. A stat replacing the original stat would make use of that option and keep the fan running.
One way to use a line stat is to jury rig the a/c so the fan goes around the line stat. You'd need to cut the wires to the fan motor and attach them to an extension cord that will plug into an outlet separate from the stat. I don't know if that's possible on your a/c. You'd need to double check every time you used it to be sure the fan is running or you'd REALLY freeze things up.
Go to Coolbot's site and read all of their stuff on building a cooler. They give a lot of hints that you might find useful in your case. They sort of tell you all the stuff you need to do if you don't use a Coolbot and that's what you need to read. I have a home cooler on the drawing board that I hope to start building shortly. I read through all of their stuff and got lots of good info. I'll be needing to buy a new a/c and I'll use the Coolbot even though it's expensive.