If you no longer have a crop in your high tunnels, then consider doing some soil building.
This summer I tried to establish a cover crop in my tunnel at the research farm, but the soil was so poor I could not keep it moist enough for seed germination.
Fall would be a good time to make some organic matter additions to the soil since temperatures are still high enough for soil microbes to be active. Just be sure to not add any materials contaminated with disease or weed seeds.
You could also consider planting a crop like spring oats, which will grow and produce biomass this fall but will then frost-kill, making spring soil preparation easier.