Here's my method and I have had very very few issues with either of our snakes in the two years we have had them. Take out of the freezer the night before and put in the fridge in a baggie. When it gets closer to time, submerge in the baggie in the straight hot water or of the faucet for twenty minutes. Take baggie out of the water and microwave the water alone for two minutes, in my microwave that gets the water to about 120-125. Put rat/s back in the water and go feed snakes.
Just one question about your setup, your description says temp is about 90. Your average temp should be about 80 and you need a hot spot at 90. 90 ambient is a bit high. You might be able to move your heat source to one end and achieve that. In our glass 40, we shoot for 80 ambient with a heat lamp and get the 90 hot spot with a under tank heat mat on a thermostat.
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