It surprises me over the years that I never though about this idea before, but when I got my first firearm, I wanted to get a hard case to go with it, and then the thought came to my head "Why don't I just store my padding in a locked box like my gun?"
I was initially hiding my stash in an out of the way place in my room that a thorough spring cleaning would probably reveal.
So I fully suggest hiding your stash in a locked box like this...
It was all of $40 to get this box with 3 matching locks to go with it.
I cannot think of a better way of hiding your stash. Unless your parents or who you live with are unreasonably snoopy to destroy your box and locks in order to see whats inside, there is no reasonable way it will be found out.
For our younger viewers there are plenty of good reasons to convince your parents you need a locked box. For me it was to store my firearm which is required by federal law and regulations to transport it on an airplane. If you don't own a firearm, you can say it is for storing camera equipment, expensive electronics, secure documents like social security numbers, money, expensive collectables you might have, or simply say it just makes it harder for people to steal your stuff.
Tip: I recommend if you get a large box like this that you have more than one place to put a padlock like mine. I saw many cases where you only have one lock and you can still partially open the sides of the box even while it's locked, for someone to see if not take whats inside.
Brands I recommend are Plano or Pelican (Although Pelican's are ungodly expensive).
Good luck out there, I hope this prevents any awkward moments between your parents or roommates.