I bought some Owens Corning 703. Now what?

Experiment to learn is good in concert with science. Did you post a RT60 ? 
Enjoy your journey:-)

how deep are the joists above ? This is a hint....

Thanks Shalommorgan and Tomic601.

Yes, I will try a few well placed panels and not go too crazy. I placed a couple panels at the floor just beneath the ceiling and really heard a difference, so I know the effort to put at least one or two up on the ceiling will be worth it. Also, there’s a lot of bass energy at the front wall.

Raise the ceiling in my bungalow. Er, um, hmm.... I hope to move into a larger unfinished basement room next to this one, 12 foot ceilings -- a blank canvas.

I somehow deleted a long post. I'll try again but keep it short.

6 x OC 703 panels will help but not all that noticeable. Buy a bunch more as they will not go to waste.

For the biggest impact look at taming bass frequencies which creates acoustic havoc in any domestic room. Make 2 stacks of 3 panels placed on either side of your system. Set these up lying horizontally at 45 degrees straddling the floor/wall corner. If you get more panels do the same in other corners. The more you have the easier it will be to see the result on REW.

The best advice I can give you is to become comfortable with REW, especially regarding the CSD (waterfall) plots. Once you begin to absorb the lower frequencies which are, because of combining either constructively or destructively, creating peaks and nulls. It is difficult to appreciate the harm done by these peaks and nulls or partial nulls. Consider that a null has nothing to contribute to the sound, it's music that's missing. Gone.

Bass can be well smoothed by using a DBA but will still need cognisance taken of the decay time. Using acoustic smoothing in the modal region in addition to the multi-sub approach will optimise what can be done. This double attack on the bass gives stunning results.

I see @ tomic601 is the only one who wisely mentioned RT60. This mysterious quantity is simply the time it takes for the sound to decay by 60dB which for the average domestic room is about 400ms. The target then is to have the full spectrum decay within 0.4 secs. REW's CSD plots provide this info.

Expect a correct RT60 to provide bass info previously missing or partially missing depending on the depth of null and more control and bass detail.
It appears poor @ shalommorgan did not go this route and required 5 iterations to get things sorted. Using REW or HolmImpulse (as used by Geddes), get the table off the net for RT60 for your size room and have fun.

The result of a correctly treated room is difficult to conceptualise but it is a bigger move to believable, rewarding and immersive sound than an expensive component upgrade. True story.

@lemonhaze
Thank you for taking the time to articulate the important things, in useful form. As the diagram on my system page will show (and which my measurements confirm) the corners are not that problematic.

( see: https://systems.audiogon.com/systems/9064 )

Given that, would you suggest 2 stacks of 3 panels somewhere else? Where the bass frequencies are the loudest? Or somewhere else?

I'm getting help with REW and learning these additional plots. I've been looking a lot at RT60 since tomic601 said that. I'll look at the things you suggest.

Posts on this site have convinced me that I'm done thinking about gear. (And I just put a system together.) So now I'm looking for a correctly treated room, or at least the path which leads there. Thanks again.