Hey,
Well, first off, you don't want to creat an over-all, temperature of 85-90 degrees, through out the cage or tank, as this would be detrimental in some respects to the health and well being of the blood. What you would rather create instead, is a temperature gradient throughout the cage, where there is a temperature on one side of the tank or cage, that is in the 80 degree range and not higher (80-82), and the other end has a slightly higher temperature of 88-90 for a hot spot or side. This would provide the blood with an option to either cool off or warm up when needed.
As for stacking of the humidity and heat, glass aquariums have what is called a low R rating, which basically is an industry term for insulation. If the tank is too large and obviously glass, then the R rating will be low, with no insulation. That is why we always suggest to would be keepers that they should stay away from these types of set-ups, when possible and use Rubbermaids when feasible and financially doable.
Closing up the top of a glass cage with some type of plexiglass can help some, if there is little to know humidity being kept in. As for the heat, that too will be affected some, but that would also depend on your heat type and the size of the enclosure. Get a piece of plexiglass cut by a glasier or your local glass cutting shop to fit under the screen, and hot glue it to the under side of the screen. Before hot gluing the plexi, you should first drill some small 1/4", holes in the plexiglass for venitilation on one side of the plexi. Give us some idea of your setup if possible and we'll or I'll, try to assist you some more where possible.
-Angel
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"Until we lose our self, there is no way of finding our self."
-Henry Miller.