ive read this thread dont no how many times trying to figure what your asking,take a pic of the building your gonna use,i might be able to help,with that keep in mind in the last 10 yrs the window units have a gas line in the bottom of the ac,water has to stay on this line,thats why they moved the drain hole to back and side of the ac,those louvers on the side has to stay open to also cool the compressor,with that the hot air coming out of the condenser on the back,if you resrtict that air flow your not gonna get much life from the unit,so build the box you speak of twice as long as your ac,funneling back and into a vent line going out,if your running that heat back into room your compressor will stay on and temp sensor will go awol on ya,a pic would help out alot here