The tarp under stops moisture coming up from the ground I guess?
how much wood is on each pallet? Maybe 1/4 cord? I suspect no more?
The tarp is 6' square. Corners folded as shown (folded under actually) and stitched so I can get my arm through the tunnel that that makes. Tarps go on top and not under pallets. Then a long loop of baling twine through the corners and around the bale to hold the tarp secure and still let air flow under it from the sides. The photo of the tarp on the ground does not have the corners stitched. That photo was the day I came up with how to secure them, and do it as simply as I could think of. I made hundreds more of covers last winter, and it became a lot of work time wise cutting and sewing. So far I've gone through a role of twine, 4,500 feet, at about 17' per pallet, and several very large tarps. Soon I will be selling firewood I covered last fall, and can begin reusing the covers, same as the pallets. The main point is however, it seems to be working very well for seasoning, and keeping leaves out as well. The only thing about ground moisture is rotting what sits on it, pallets included. So far no indication of this, but one year is too short of measure to judge yet on the gravel. Gravel does hold moisture well when shaded.
Each pallet stacks to a little over 1/4 cord. Four of the drums used for palletizing a cord equals 226 cu. ft. loose thrown. (well over what is commonly thought to be 180-200 cu. ft. loose thrown per cord)
I'm not saying, or implying, this is the fastest way to season firewood. It is working about the same as the large racks I was using if they were covered. Uncovered in both cases, the pallets are much better. The firewood in the racks was tightly stacked three rows deep, and uncovered the top half of the middle row I found to be wet and heavy when delivering even after a year, from rain/snow and lack of sun/air.
I think the fastest way to season is to process (cut/split) in March/April/May. I keep looking at the wood I did this past spring, compared to last fall, and I don't see, feel, or hear much difference.