ACs are also great for storage. This one needs some items stored on top. When my mother kept kids, she placed wet and soiled pampers on top of the AC. My father stored stuff there. I had central heat and air installed after my father passed away, and I have not yet removed the mounted AC. I have an old bag with a little bit of Miracle Grow, lighter fluid, paint scraper, and sometimes a bag of charcoal on top.
When it is hot and you decide you want that cool air RIGHT NOW, you will get creative and figure out how to balance the a/c (swamp cooler in the case) in the damn window!
Worry about mounting it right when you need the table for something else!
(yes, I have used this method before, no I am not White Trash, just resourceful!)
Oh, if it is a rental and you can’t fasten to the wall anyway, sometimes the stack-mount is good enough for a couple of months until it cools down!