Nope you are still not getting the math right. There is a 4.5 psi differential with a relative constant temperature, actual 20 degree drop with 8k altitude increase ( 52 degrees to 31 degrees).
An actual 52 degrees at 2k to a very reasonable actual 81 at 10k would be a 50 degree relative raise.
I already conceded your 50F rise, and showed that it might make 0.5psi difference, not anything significant.
But since you mentioned math, let's discuss it in a bit more detail then. The 4.5 psi altitude pressure differential is based on the scientific definition of the standard atmosphere, which I suspect you are familiar with. Its defined as 59F at sea level and 14.7psia, and the temperature is expected to drop by approximately 3.6F per 1000 ft elevation gain. So as you say, 52F at 2k, but about 23F at 10k (rather than 31F).
As the temperature drops with altitude, the air density determines the rate of the pressure drop, and the temperature of the air (along with pressure) determines the density of the air. So if the air is significantly warmer than the standard atmosphere expectations, the pressure drop will be less than expected because the air is less dense than expected over the altitude rise. So, if you are operating in an environment where the temperature at 10k ft is 81F, and the standard atmosphere expects the temperature to actually be 23F, let's do a quick and dirty calculation to approximate things.
The average temperature from 2k to 10k would be expected to be (52+23)/2 or about 37F. The actual average temperature would be (52+81)/2 or 66F. To compute the difference in density we need to convert to degrees Rankine, so we add approx 460 to each of them. So the air is less dense than the standard atmosphere by the ratio of 497/556 or almost 12%. So the expected 4.5psi delta would actually be about 4.0psi, plus about 0.8psi difference because of the 30F actual temperature rise when the air went from 52F to 81F (541/512)*14.7 - 14.7.
So whichever way you want to calculate it, we're talking about 5psi difference, which isn't much. Since I can't claim to be an expert on waterproof bag design, I'm not saying with 100% certainty that the bag shouldn't explode, but it seems reasonable to expect it not to under these real-world conditions in which it could be used. As I thought about this a bit more I googled and found that regular birthday balloons can rise to 30,000 ft before they pop (there were studies done on this with respect to them interfering with aircraft traffic). I'd expect the bag to be more durable than a penny birthday balloon, but I could be wrong.
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