I've noticed over the years that 2 issues exist where I store split wood. My main area is close to the Mississippi river, thus, basically an old sand bar that provides really good water drainage so just using pallets directly on the ground works fine. In my other main location, the ground is a heavy clay soil that doesn't drain well so I use old 6x6's under the pallets to get them off the ground further, providing more area for air to flow around the stacks. I usually am only 9 months ahead, but I supply camp fire bundles so moisture levels down to the 20-24% are okay for me.