I've never considered planting as a permanent cover, but it's a great idea. Since this is presumably in or near a wet area, consider whether any plants are considered invasive in your area and avoid them. A story circulates among salt marsh restoration folks here in Maine about a project to eliminate phragmites, an invasive marsh plant that does well in areas near roads and can outcompete spartina and other native marsh plants. After a day of planning a major herbicide treatment in an attempt to eliminate phragmites from a marsh, they returned to the boat ramp where they were met by a duck hunter who had grassed his boat completely with phragmites at its mature, seed-dropping best! It was fantastic cover for the boat, and I am sure it hid well in the areas of the marsh where phrag was already established, but also a seed source to spread the invasive all over the marsh. Most fresh and salt water marsh plants are pretty low here, so blinds in the open are often camouflaged with upland plants to make them look like small hummocks that are growing shrubs or trees instead of marsh grasses. A common camouglage for larger blinds in the salt marsh is to drive small to medium sized saplings around them. The leaves fall off, but just the bare stems around the blind are pretty effective, especially is the lower portions are enhanced on each hunt with a little seaweed and loose grass.