Sub placement is always interesting as the low frequencies interact with the room’s shape and size as well as the Sub’s placement. Along a wall, away from a corner is likely to give you a more even sound level at all room locations. Near an open doorway can reduce the Sub’s sound levels over a solid wall. In a corner will usually reinforce the Sub’s output but can lead to uneven sound levels in other room locations.
I’d try each likely location and play a selection that is heavy on the low frequencies, then try your various seating positions to see what sounds best. Once you have it down to a couple positions you like compare them while moving around the room and go with the one with the most even sound.
If you use an extension cord for the Sub you can do this a lot faster than plugging / unplugging it. Do use a reasonably heavy cord so the Sub isn’t compromised by any voltage lost to a too-small cord. I have one of my Subs on a 20 foot extension, #14 wire.
If you are going to do Trueplay, probably save doing that for the top few locations as it helps but isn’t a cure-all.
I went with corner locations for both my Subs, the media room gave me little choice as it is diamond shaped and behind the TV cabinet was the only spouse approved spot. In my office, I tried a corner to start with and it sounded so good I never bothered to try the other two possible locations.