Sub at the weakest bass point in a room?

Yes but this is only the first step. With the sub at the weakest bass point it will then become the strongest bass point. The next step is to put the sub at the new weakest bass point, making it the strongest bass point. Crawl around until you find the new weakest bass point. Move the sub. Repeat until you get so sick and tired of moving subs around that you buy a DBA.

If this is your only sub, then you are going backwards. :)

Put the sub in your listening location, and measure the bass at your possible locations.  When you find the location with the smoothest bass, that's where you want to put your sub.

If this is your first sub and you are placing a second, then your approach is correct.

Also, remember that bass traps and EQ help fix what placement cannot. I wrote about this more here:

https://speakermakersjourney.blogspot.com/2020/04/how-to-not-buy-subwoofer.html

What Eric said.
While your sub is at the listening position map out all the locations where the bass sounds strongest. 
A cheap dolly from Harbor Freight could save your back. 

Get sliders (Harbor Freight) to get them it (them) placed. When your done with the major moving, remove two and leave two, for the final placement.
I can move 200 lb pretty easy, with just a heal bar (crow bar) and one slider, like a 5th wheel. Then use the heal bar to remove the last two when your done. I leave  two.

On rough concrete, I just use 1-2" dowels, a few inches wider than the bass bins..

A single sub can add a lot, with placement.. It can also cancel/comb at the cross over points.
  
With DSP/phase correction, either, on board or passive, via OXO, placement can be pretty precise. With an active mic being used
for real time correction, you can hear the distortion, being cleaned up and more than one note can be heard, in REAL time.. Kinda cool really..
Know your room, AY.. 

and then there are Columns... COLUMNS. . . . .C O L U M N S.....

Regards

LoL @ millercarbon.

You should have added or until you decide to just buy speakers that play lower or until you’ve sold yourself on the idea that bass isn’t that important...

What’s really funny is no one wants to admit what I said is true. Their solution is sliders so you can fail more times before you get tired. Oh and of course how not to buy EQ and GIK. At the very least they should recommend something that might actually provide really powerful and perfectly smooth bass like put the sub in the middle of the room and sit on it.

Miller is the most important advocate of the distributed bass array cult, and he's' exactly why I won't engage with any of them.

Oh, great! Another cult. Just what we need. 😬

thanks Eric,
I do have a second sub (both Velodyne DD15), but one is out for repair. I thought to put one in the center, and when the other comes back I will place it against the wall behind the speakers, but off to one side.