The ones I have constructed/lived in have a hole you slither into. The entrance is camoflauged, but you only go into/out of it one time each. You typically do thee under the cover of darkness, preferably with no moon. That all being said, you also have dirt you need to conceal. Top dirt is almost always lighter in color than the deeper stuff. You have to spread it over quite a large area to effectively hide it. Normally, these are constructed by 4 men-keep that in mind. It spreads the work out.
A quick, effective cover for the bolt hole is a poncho-but it has to be kept tight. Fluttering causes noise and, if it breaks loose, its a flag.
There really is quite a lot to think of with these. You have to consider shadows, terrain, orientation to your target, distance, etc.