You didn't mention species of inhabitant.

>>1) Having glass cut to fit into the 4 rectangles on the top cover to better hold in humidity.

Any local glass company can cut you glass to fit the top. Additionally big box stores stock 2.5mm or 3/32" glass up to 36" in post cases. As well as the tool to cut it, as well as sanding stones to smooth the edge. Cutting a piece to cover 90% of the screen top will increase humidity and air temps within the enclosure. Leave a small strip of exposed screen at the front or rear to create a draft effect for air exchange.

>>2) Room that I keep the tank in has a tendency to run lower on temperatures as well as humidity.

I despise under tank heaters they do more heating the shelf than the animal's space inside. Consider using a Radient heat panel or choosing a species that doesn't need a high basking temperature.
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Jeremy Payne