Drop ceiling in attached garage to help retain heat during Wisconsin winters?

Hey,

I want to use my garage more during the winter. I'm hoping to maintain somewhere around 45-50F, just enough to be above freezing and be generally usable for projects. It's a 2 car attached garage. I've already got drywall up on the walls (will do blow-in insulation next), but the ceiling structure doesn't really accommodate 5/8" drywall.. I'd need to add extra joists or something.

I already have all the drop ceiling tiles and hardware I would need, so installation cost is minimal, but am I setting myself up for disappointment given there wouldn't be a non-permeable barrier or seal to effectively stop heat from escaping? I could add fiberglass batts on the top of the drop ceiling tiles?

I'd use a diesel or electric heater when I want to use the space. Aside from that it would be unheated.

Thanks.