Is it a bad idea to install real hardwood over a crawlspace. We found some nice gunstock maple that we like for a good price. I live in St. Louis area. It is a vented crawlspace. I plan to put 6 mil plastic over the dirt ground.
I have solid hardwood that I installed over my crawlspace back in the 80's. There have been absolutely no issues at all. My crawl space was vented with a concrete floor. I have since closed off the vents and insulated the rim joists and it stays nice and warm now. If you seal up your dirt floor properly with 6 mil plastic you should be fine.
As long as you have no standing water down there and a full poly vapor barrier on the ground, you should be fine. All hardwood flooring manufacturers should have this information and any other site requirements in their instructions.