We dry our wood outside, strapped down to big 6x6 dunnage to keep it flat, covered by tarps over the top (not down the sides). In the PNW its pretty wet all winter, so we typically figure about a year of drying per inch thickness for softwoods (cedar, fir, maple etc) to get the moisture down to 10-12% ish, which is as good as it gets without bring the slabs inside the heated shop. The wood still moves as it adjusts to finish and humidity of its final location (I've shipped some finished furniture to the prairies, where its very dry, and the wood (sealed, with a good finish on it) has checked and splits have opened up, even though it was stable when I was started working on it. Sealing the ends of the as-cut slabs with anchor seal seems to work good, but we almost always get checking or large splits in the heart wood on the larger slabs. Not much you can do when the tree has internal tension. I can confirm that you need good circulation and dehumidifiers, we had a couple slabs stored in a buddies garage for a couple weeks and it developed mold almost immediately.