After years of somewhat janky solutions, I'd like to figure out the correct way of installing a window air conditioner in the window of my office. The windows are probably not original to the house. They have a plastic frame. From the side, the profile would look something like this:
That is, on the inside, the plastic frame extends up about an inch above the wood sill. There's a second thin strip of plastic that seals the window on the outside when it's closed, and it's a chunk shorter. Beyond that, the plastic frame extends beyond the wall (so there's not really a solid surface into which things can be screwed on the outside).
What's the correct device for mounting a (small-ish) air conditioner in this window? A lot of them seem to assume you can lay a flat surface across the bottom of the window from the inside to the outside, but that's not the case here.
I've tried something that looks like this, but it never really seemed to work: it was fiddly to install, and never really seemed secure. We haven't had the a/c fall out or anything, but I'd like to figure out how to do this right.