South Maryland should offer a climatic zone that makes being concerned about your JM's in winter more or less unnecessary. Just make sure any containerized trees have adequate protection around the root zone - that is the vulnerable part of the tree and roots do not tolerate temps below around 25F for any length of time. Either sink the pots into the soil, wrap the pots liberally with bubble wrap or store where temps remain cold but not much lower than freezing. Top growth should be unfazed by cold or at least the cold you are likely to experience.

And never fertilize in winter. The trees cannot process it while dormant.

"Should" is always such a good word, isn't it?
I've always done as you suggested, but have also had a few casualties each year. Now, knowing what I know about soil, perhaps I can stave that off.

Planted a Rose of Sharon, a gorgeous red hibiscus, 2 different trumpet vines, a 'Gabor' lilac, and repotted an 'Inaba Shidare,' my 'Inazuma, 'and an 'Autumn Moon.' Going to try to do a few a day, rather than exhausting myself in November and missing some that direly need it.

If you have had difficulties in overwintering JM's in the ground in zone 7, it's not been due to cold. Some other growing condition - poor drainage, other soil issues, lack of establishment, inadequate water, etc. - is causing the problem. Heck, folks get these trees to grow and survive in zone 4!

Containerized JM's are quite different. Without that insulating mass of soil around their root zone, they are very vulnerable to cold damage. The roots are very sensitive to damage below 25F. The larger the container, the less pressing this issue is, but I would still group all the containerized trees together at the very least and shield their roots from cold as best you can.

Yes, I do group them and mulch around them. In my repotting efforts, they're all going to much bigger pots than I've used in the past. I am convinced it's the drainage, given the fact that I didn't know squat for way too long about my babies and their need for oxygen.

The last 2 years we've had colder than usual winters. That probably didn't help.