Gordon,
I used to own a company that did crawlspace encapsulation as one product offering. It's the real deal--we started by laying down drainage mat, then covered it with 20-mil fiberglass reinforced plastic sheeting glued together. 10-mil plastic went up the sides, glued and pinned to the concrete walls just below the floor joists. We'd then hang a permanent set-and-forget dehumidifier from the joists, set at 50% RH, with an outside drain. For chronically wet spaces, we'd also install a sump system, or integrate an existing sump into the system. We guaranteed the work against water intrusion for 25 years.
Besides reducing indoor air pollution (50% of the air you breathe is from the crawl, including vapors from whatever is living down there, peeing and pooping down there, and dying down there), it also controls interior RH. In houses with moisture problems that cause the wood flooring to get wavy, the system can reduce RH to the point where the flooring sits flat again. And indoor mold growth can also be better controlled (mold does not grow at less than 60% RH).
I arranged to have all the local west coast installers become certified by installing the system at my house. It changed a dark, dank crawl into 1000 sq ft of usable space. The plastic is white, so it looks like an operating room down there. Really a nice upgrade.
The process is called AdvantaSeal, and the company is AdvantaClean. In Charleston, the local AdvantaClean is run by a friend of mine, Mario Colangelo. I know that he does a lot of these.
https://www.advantaclean.com/charleston-sc/ He's a great guy, and can give you all the details.