It will work if the part of the A/C that installs outside the window is outside the wall of the RV. Tucked fully inside, trying to operate in a closed space behind a refrigerator intake vent can be a problem, heat is still trapped inside, concentrated in a smaller space. You might be able to get enough air to the "hot" side of a window A/C with ducting and additional fans and blowers, depending on the air flow configuration, but just sticking it in that space likely won't work.
There are RV wall units configured differently, with only a few inches sticking out. The Cool Cat is one frequently used in very small RVs, but comes a RV price, and I don't know if there are any models large enough to cool a 5er in Oklahoma in the summer sunshine, since a 15,000 BTU/hr A/C doesn't keep up with that heat load in my 30 foot motorhome.
