I've already insulated 3 side of my 20 gal tank with foam board. My temps are still fluctuating thought. I take it, its my screen top. I've used Argentra's method of foil treatment for humidity. What can I add on to the top that can help insulate?

Also, it isn't a sliding or locking top, its the kind that goes right on top of the enclosure. Due to this, there is need insulation around the edges as well.

If anyone could help me I would appreciate it.

-Zack