What process did you use to integrate multiple subwoofers for 2 channel listening?

Today I will be trying to integrate up to three subs. Two are matching Rythmiks F12SE, and one is a REL R-328. The Rythmiks have a variety of adjustable parameters, including phase, crossover, and gain. There are other switches and passes on the sub, but I'm going to try to keep it basic to begin with. The REL has variable gain and crossover; the phase on REL is either 0 or 180.

I have REW for measurement. I will be buying a few more furniture sliders this morning, on doctors orders. ;-)

QUESTION: If you have multiple subs, by what process did you integrate your subs? One at a time? More? Which adjustments did you try first and in what kinds of increment?

I know that trial, error, measuring, and listening will all take time. Rather than look for a needle in a haystack, I'm curious what sequence or process was most effective for you.

Thank you.
Sarjan at 6moons has several articles and reviews on integrating subs that are very informative, cutting through all the bunk. John Darko has done similar work as well and he even has videos about his quest to properly integrate his sub.

Worth checking out.

All the best,
I used REW for 4 subs. First I setup the front 2 by themselves and then the back two separate to make sure volume, frequency response was similar and then all four together. 

Thanks. I have 3 subs. @millercarbon, I'm not sure what mistake you're trying to disabuse me of, but all I mean by integrate is make them sound good. Some of the technique won't just be listening but much will. From listening to moving/changing to measuring back to listening. 

you can set the crossover to about 80 and then adjust the volume levels.
That's a helpful bit.

@nonoise  Thanks for the reference.
@mmcely Thanks for sharing your technique concisely. I'll try it.

Just after I posted this, I found this very helpful and detailed discussion: https://www.thehifipodcast.net/episodes/episode-24-how-to-integrate-subwoofer

I set up mine the old fashioned way - I put sub #1 in my listening position and walked around close to the walls while playing a track with deep bass.Quickly found the two corners where the bass was best and set them up there. Then it was a matter of trial and error over the next few days adjusting the settings.
I eventually moved one to a "null" corner firing towards the peak corner where it previously resided.I think it's smoother that way in my room. They are both behind me in the back corners totally unobtrusive. Anyone listening to the system marvels at the bass the little Harbeths kick out (heh,heh).