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.