6 An individual may store a restricted firearm only if
(a) it is unloaded;
(b) it is
(i) rendered inoperable by means of a secure locking device and stored in a container, receptacle or room that is kept securely locked and that is constructed so that it cannot readily be broken open or into, or
(ii) stored in a vault, safe or room that has been specifically constructed or modified for the secure storage of restricted firearms and that is kept securely locked; and
(c) it is not readily accessible to ammunition, unless the ammunition is stored, together with or separately from the firearm, in
(i) a container or receptacle that is kept securely locked and that is constructed so that it cannot readily be broken open or into, or
(ii) a vault, safe or room that has been specifically constructed or modified for the secure storage of restricted firearms and that is kept securely locked.
I'm guessing you got stuck on wording of 6(b)(ii) where it says "specifically constructed or modified"; which very clearly means that the room you're using must be able to satisfy the requirements, which you may have to specifically construct or modify so that it may 1) securely lock, and 2) not be readily broken into.
Very simple. Very clear.
readily, adverb Without hesitation; willingly. Without difficulty; easily.
For example, if you have a heavy metal grate for a door that has a big old secure lock on it; but the bars on the door allow you to reach through and unlock the door from the other side, that door is "readily broken into".
If someone has to kick or punch through the drywall on a typical home construction, and make the hole bigger and bigger until they fit, squeezing through or getting their arm around to unlock the door; that's not fitting the definition of readily.
If they have to bring tools like a crowbar, again, not readily broken into. Just make sure your door isn't made of paper.
But the TLDR is, are you more concerned about the law or having your firearms safe from theft? Because if you're worried about the law, you're thinking too much about it. If you're worried about theft, you'll be miles ahead of any requirements and need not worry one bit.