A lot is going to depend on WHERE you camp. Trees and wooded areas? Wide open without a tree to be had? We had our 23SS for 7 years and used it regularly, 2 - 3 x per month, without any hesitation. Trees and shade make all the difference in the world. 99+% of our time we had lots of trees and it was perfectly comfortable. Granted, we had the A/C when we needed it and used it most of the time in the summer. Spring and Fall camping are awesome. Plan on staying home in August unless you really enjoy sweating, but that's the south! Never a problem with water intrusion when closing up based on the way the tentends on the ROO/Shamrock are designed...just be sure to close your windows in the tentends. Yes, still applies that you open up and allow to dry completely when you get home.
We left only minimal water in the FW tank to use on roadside stops. On one occasion when we did have a pretty full tank we noticed a funky odor about 3 weeks after returning home. Discovered it was the water. Suggest you just reach under and drain the FW tank when you get home and problem is solved. Never had a problem with mildew or mold.
The one time our A/C would not keep up with the heat was in Vicksburg, MS....you could almost SEE a shade tree, but that was all. 99+ degrees and 99% humidity. Miserable. We made a Walmart run for an oscillating fan. No big difference until the sun went down and then life was good again.
You didn't mention where exactly in the SE you may be heading and that can change the whole story. Based on our camping in West TN, middle TN, NE GA, FL, northern AL, KY, LA, I would not be concerned. If you're near the ocean or gulf you're going to have breezes that are very nice. Hybrids are not #1 on the list of trailers here, but don't think it has anything to do with the weather...it certainly didn't make any difference to us or others we know. Remember that with a HTT, you can unzip and have fresh air coming through. Many TTs are more like being in a box.
If you don't mind listing more detail on location, you may get more complete answers, but at this point I would not stick a For Sale sign on it.