My guess is that the humidity in the crawl (since it's vented to the outside, thus, I'm assuming it's unheated), is being drawn up into the living space since there is no vapor barrier/insulation under the floor. Depending on where you live, you may be able to close off your crawl vents (either permanently or temporarily, depending on the season. Do check into this if you can.) I would think that if you just insulated the floor with fiberglass batt insulation with a build-in vapor barrier, you may be OK. I live in the NE. My crawl is vented and unheated. My floor is insulated and has a vapor barrier on the INTERIOR subfloor (since the barrier is part of the fiberglass batt insulation.) I have not moisture or mildew or mold problems.
Keep an eye on your post for a short while. 'Others' will happen along to give you more feedback. I commend you on your 'mitigation measures' to prevent water from entering your crawl.