What type of floor is in the crawl space?
Plastic vapor barrier laid over pea gravel.
If you want to really do the crawl space properly you need to redo the plastic sheeting with a proper vapor barrier for the floor and walls with everything taped and sealed. A lot of work. Not cheap to hire a pro. In my crawl space in my DE home the height is between crawling on my belly and crawling on my hands and knees.
Once done properly then a dehumidifier can easily bring down the RH to 45% to 50%.
And if you do all this you might as well have a basement. Here in our part of Indiana basements can be fairly rare, Many crawl spaces I have been in, which numbers at least 200, have had moisture issues and a shoddily installed vapor barrier with pea gravel on it. My favorite one had a sump pit in it which was in the higher part of the crawl so water ran away from it and it had no drain tiles running into it so it was effectively useless.
I have been in one that was completely sealed with a pool liner like material, it was clean, dry and conditioned. Once you factor in the expense of doing this plus the expense of conditioning it, I figure you might as well have a basement, even if just for storage.
In the heat of the summer most crawl spaces here have moisture condensing on almost everything it can. IMHO here it is just to cold and damp and hot and humid most of the time to have a crawl space vented to the outside and not expect moisture in there. It gets so ungodly humid here its ridiculous.
What aggravates me is the work is a lot easier and cheaper to do if its done right after the block is laid. but its seems like out of sight out of mind when they build these homes and someone 15 or 30 years later has to deal with the problems the poor preparation creates.