I share your delima ,and i'm upstairs to boot! It got mighty old toting all that crap up here in the past. The last thing I would never do however is be dishonest with my landlord, as we may use the building as our homes,however under no means is it our property to do with it as we wish. That said, most folks who hear the word hazardous material think its harmful to our health. Show them the gear, attach a regulator, take a few puffs of "air" and show her its completely safe to breath. I would not suggest using helium. Lol. Be sure to explain the purpose of a burst disk as it relates to a fire etc. You may also win some points by comparing these to the 100% Oxygen bottles in which many medical patients use, then of course mention that these are way below even the concentration of those. Educate them as to what you have, ensure to them you will take extra precautions to ensure no damage is done to the walls or floor etc.
Renters insurance would be a must for me in this instance, but in reality you should have it anyhow as most places are pretty cheap. In my case, I use a dive trailer and have to deal with the hassle's of parking etc, but then again, when I come in late from a weekend of diving, I simply lock it up and get my but in bed. Quite honestly the trailer was one of the best purchases I've ever made next to my first cylinders. Home owners have their garages to piddle in, I have the dive trailer. I'm out there doing something in it a few times a week at least.
As a second alternative to a trailer, you may consider renting you a small storage building for about 45-50 bucks a month to store all your gear in. Sure as heck better to stink up a storage building than your bathroom. Just make sure you check your booties for critters before the next dive!!!!!!!
Safe Diving,
Kenny