Is a lease not a voluntary contract? And by signing it has the individual not agreed to the terms and conditions specified?
No. It's not legally binding to tell someone what they can or can not do on a rented property so long as what they are doing is legal and does not damage the property.
For example, you could rent an apartment or house and the lease could say no overnight guests - not binding - not valid.
It's a way of not turning renters into the slaves of the landlords.
If you were renting a room in a house or apartment it could be different.
If all the landlords put this in their leases then the only people who could own firearms would be homeowners.
In this case, seeing as there was a heated argument and all, I'd say moving your firearms temporarily isn't the worst idea. What you really need is a friend you can trust with an RPAL. A storage locker isn't going to work.
In BC it's really easy to call the CFO and tell them you're moving your stuff to such and such and address and they'll call the friend who has the RPAL to confirm it, and issue the new paper work.
It can even be done for a friend without a PAL if you use your own safe, and he or she does not have access to your safe. Best in that case to spend the money you would have spent on storage to get your friend an RPAL. It'll go over easier as well when you call the CFO and tell them that your friend's application is in progress.
I don't know where you live, I'm only talking about BC.