Insulation will not effect humidity much. It does go a long way to helping with ambient temps. Personally I use ridged foam insulation. It is available in many thicknesses but there is a 1/2 inch one that does not have link together edges I like for this tanks it isn't expensive and at 1/2 inch not too bad to cut and is enough insulation that it makes a big difference. I just cut it to size and tape it into a 3 sides box and place the tank on it (bottom back sides) the top needs something and the front you want to see into. But it will not alter humidity.
glass holds heat better than most plastics. Thermal mass basically not completely but for the most part work by how heavy something is glass is heavy and once warm does not give it up quickly. Slow to heat slow to cool.
if you are not interested in humid hides a side turned tank can also work well it is much more work than hides however.
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