I feel ya. I only own a 160gb PS3 and having to erase games and installation data is always a hassle. I can't imagine having to share a console with someone though. That's gotta be part of your problem as well.
At one point in time the only PS3 I had was a 12 GB. My original PS3 had broke, and I didn't fix or replace it until I needed to. The day Dark Souls 2 came out was the day I decided to remedy the situation, and I did so by opting into the cheapest SKU I could find, and it was a 12 GB Super Slim, which I think was around $200 at the time, plus the cost of the Dark Souls 2 game.
I really regret that purchase. The 12 GB limit sucks, but even worse than that is the fact that the damn thing started crapping out on me after less than a year. The system still works, but every so often the fan within the system will become extremely loud... and I mean LOUD... Something is loose and it's probably a simple fix but I haven't bothered to acquire the tools to do so. (Since then I bought a co-workers PS3 for $50 along with controllers and a dozen or so games a couple years ago).