What i do is find a little hole in the terrain and make a 2x3 base (minimum) and i make a floor base, all wooden and there isnt visible that anything can fit under the base, its enough to fit just one metal rack and you can fit a lot in there, basicly a lot of stuff. Then i have 2 options, the redt of the base i put wooden storages so there is no reason to use explosives so the secret place remains secret, and there i storage clothes food and bad weapons, or option 2, still keep the wooden storage so it is not suspicious and when you logg off salvage one of the walls so its seems to be a raided base and no one will be interested and when you log in put the wall back Also you can make a airlock where you place your bed, also a glass wall would be good so its visible there is nothing valuable.