VanillaPlus/temp/blockmodels/vertical_mossy_cobblestone_slab.json

{
  "parent": "vplus:block/vertical_slab",
  "textures": {
    "bottom": "minecraft:block/mossy_cobblestone",
    "top": "minecraft:block/mossy_cobblestone",
    "side": "minecraft:block/mossy_cobblestone"
  }
}