When I lived in a rental house I had a small Sentry combination fire safe I bought for 180 bucks on-line and then bolted to the floor in the bedroom closet.
It only came with 2 shelves, but you can buy more from Sentry. Four shelves will fit 8 semis in this tiny little safe. I used a trigger lock for my shotgun and kept the key in the safe.
Oh, and get a case of dessicant packets from amazon and scatter those little critters around liberally so your guns don't rust. Even "airtight" safes can be moisture wicks because they're a lump of steel.
I bought a proper long gun safe when I got my own house.