Hi Tom,
Apologies if I repeat myself...I thought we covered this on another post?
The risk of them getting "rewetted" is to high by leaving them out, though some have tried this and often failed. Tried and true traditional methods seem to be the best. Once the harvest is over, the straw (not hay) is baled and stored in 'drying barns' to further cure in most cases. Some builders have considered, and from what I understand a few have tried to use commercial lumber kilns to further dry the bails but the added cost in handling and shipping does not warrant such extreme expenditures.
So, for the most part, you are going to buy your bails direct (most cost effective) from a farmer or distributor and or through the straw bale contractor hired for the project.