I just bought a 1.5" pipe flange from Home depot, I took the mount in the store with me and found the one the mount would screw into the most. Then I coated the threads with Loctite Threadlocker Red 271 and tightened it as tight as I could get it. Between the mount and flange was a section of thread showing, so used a piece of plastic pipe to fill that gap.
I used a 1" hole saw bit, marked my center and drilled, mounted flange with mount and installed camera pushing all wiring into ceiling.I caulked the top of flange before install for added weatherproofing.