From my experience you might find saran wrap taped over card board works a little better than tin foil. Tin foil seemed to just reflect the heat more or something, it didn't seem to lock in the moisture like the saran wrap did for me. Some people eventually use plexi-glass I think.
As of now I have Styrofoam completely wrapping in 3M silver metal tape (3350 ) which looks like tin foilBut it seems to be working ok. I guess I could wrap them over with saran wrap. Might just do that in the next couple of days. Thanks.
ps. I would go ahead and move the snake and check the glass temp. If the substrate is 90 the glass might be too hot. And then measure the glass temp. set the thermostat to 90 and work up slowly checking the glass and then waiting. Best to do this before the snake is there at all. But guess you'll have to work with it. I wouldn't let the glass get over 90 But you will probably end up setting the thermostat higher than 90 to get the glass to 90. Make sure the temps stabilize before changing the thermostat setting.