I would put down at least 3" thickness and maybe thicken it around the edges if you're intent on concrete. No mesh--it's taking no weight.
Better yet, just grade the area flat and put down a few layers of preformed foam insulation cut to fit tightly. You can do it on the floor and on the walls.
Lay a sheet of 1/2 OSB or ply on that and you'll be good to go for storage.