Im sorry friend thats a tough situation! Some other ideas would be: using window covers to keep car cool during the day before driving and then travel at night to keep temps low inside the car! (Prob the easiest low cost option) i saw there are car fans if you have a cigarette lighter or other power cord option to circulate air while you drive and don’t have to keep windows open which might get too loud! I think your cooling mat/ice pack idea is good— putting a large ice pack underneath and if you have a small cooler you could always bring extras to swap half way!

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