Don't worry bud, the people that would of mocked or took a stab aren't around the forum. stir :eyepoke: :angel:
This is what I was going to say, in summer the display case would be fine, your spiders should enjoy the outside air.
The only issue with winter would be the cold, the fact is this, even if you give every spider a heating pad, the cold will still be to "strong" or overwhelming. Also glass wont help keep it warm inside, as glass takes on the cold.
Different story if you have a room that the cabinet is in and not exposed directly to the elements, the zink sheeting and open sides will add to the cold or you can insulate your your cabinet and have a blanket hang over the the front side.
I know from experience that this works, I had my spiders housed in a cabinet, and the cabinet was kept in the flat that had tiled floors and zink roof, and I would put a sheet of polystyrene in the front and hang 2 to 3 blankets in front of the cabinet with a heating pad per shelf
You can do a test run and see what comes from it.