I’m not sure about where to buy the food grade plastic (although the inside of a potting soil bag should be fine to use), but the black spots at the bottom of the peppers is almost certainly blossom end rot. This happens when plants like peppers and tomatoes are unable to take up enough calcium. It’s not actually caused by a shortage of calcium in the soil, but rather due to irregular watering which disrupts the nutrient uptake. Keeping the soil evenly moist should resolve the problem.
I’m not sure about where to buy the food grade plastic (although the inside of a potting soil bag should be fine to use), but the black spots at the bottom of the peppers is almost certainly blossom end rot. This happens when plants like peppers and tomatoes are unable to take up enough calcium. It’s not actually caused by a shortage of calcium in the soil, but rather due to irregular watering which disrupts the nutrient uptake. Keeping the soil evenly moist should resolve the problem.