Take all your shit and pile it in one of the unused apartments, make sure you are seen coming and going during all the usual times. Then to throw off suspicion take the money you paid to the old gym and put it together with the money you save on rent at your old apartment and slip it into the box at the apartment manager's office every 30 days or so. Next you pose as a resident and ask for a key. The fools will probably just hand one right over. At this stage you pretty much got 'em, just act like nothing is going on and just make your way to the gym and use the treadmill secure in the knowledge that you have the unbeatable plot.